What is vestibulitis? How is it managed?

Vestibulitis is defined as a constellation of symptoms and signs, including entry dyspareunia, vestibular erythema, and vestibular tenderness in the absence of an active dermatosis or disorder that would otherwise explain the findings. Management includes symptomatic relief with 5% lidocaine ointment; tricyclic antidepressants may be helpful. Surgical treatment should only be considered in severe cases that are refractory to medical management.

Benign Lessions of the vulva and vagina

Reff: GENERAL GYNECOLOGY AND INFERTILITY > 1 BENIGN LESIONS OF THE VULVA AND VAGINA

What is the vulva composed of?
The vulva is composed of the labia majora, labia minora, mons pubis, clitoris, vestibule, urinary meatus, vaginal orifice, hymen, Bartholin's glands, Skene's ducts, and vestibulovaginal bulbs.

Name the five disorders in which infectious agents cause lesions of the vulva.

• Chancroid (Haemophilus ducreyi)
• Syphilis (Treponema pallidum)
• Lymphogranuloma venereum (Chlamydia trachomatis serovar)
• Human papillomavirus
• Genital herpes 

 Describe the clinical features and treatment of each disorder listed in question 2.

Chancroid: Sexually transmitted with an incubation period of 3-10 days. Presents as small, tender papules that soon break down to form ragged, tender, nonindurated ulcers usually located on the labia, fourchette, perineum, and perianal areas. May be single, but are more often multiple.▪ Treatment-current drug of choice is erythromycin.

Syphilis: Sexually transmitted with an incubation period of about 2 weeks. The first lesion is a macule, which soon becomes papular, then ulcerates to form a primary chancre. Classic description of the primary chancre is an indurated, painless ulcer with a dull red base. If untreated, primary stage typically lasts 3-8 weeks and then the ulcer spontaneously heals. In secondary syphilis, skin rashes may be macular, papular, papulosquamous, or pustular, and any of these may occur on the vulva. Condyloma lata are seen in secondary syphilis and are characterized by confluent, spongy, gray masses with flat tops and broad bases located at the periphery of the vulva. In late syphilis, vulvar lesions termed gummas appear as squamous lesions or subcutaneous nodules that sometimes ulcerate.▪ Treatment-remains penicillin for all stages.

Lymphogranuloma venereum (LGV): Rare in temperate climates. Incubation period is between 3 days and 3 weeks. The primary lesion is a small, painless papule, vesicle, or ulcer, typically located on the fourchette but may also occur on the labia or cervix. The secondary stage is characterized by enlargement of the inguinal glands to form a painful mass, which tends to suppurate and form sinuses.▪ Treatment-early LGV responds to tetracycline. Prolonged treatment may be necessary.

Human papillomavirus: Sexually transmitted with incubation periods ranging from 3 weeks to 8 months. Manifest on the vulva as genital warts. Commonly are papular, appearing as small, raised, rounded lesions, usually multiple. However, may present as condylomata acuminata, which are irregular, fleshy, vascular tumors affecting any part of the vulva.▪ Treatment-repeat application of trichloroacetic acid, podophyllin, topical imiquimod (Aldara), cryotherapy, or laser surgery.

Genital herpes virus: Sexually transmitted with incubation period of first attack usually 2-10 days. Lesions are initially vesicular, but rupture to form single, multiple, or grouped shallow, tender, ulcers, 1-2 mm in diameter. Lesions are most common on the labia majora and minora, clitoris, perineum, and perianal areas.

Treatment-acyclovir is the drug of choice for the treatment of outbreaks. However, it does not influence the rate of recurrence. List the common cystic lesions of the vulva and vagina Cysts of epidermal origin: sebaceous cysts, epidermal inclusion cysts, hidradenoma Cysts of embryonic origin: Gartner's duct cysts (arise from vestigial remnants of the vaginal portion of the Wolffian ducts) Duct cysts: Bartholin's gland Cysts of urethral and paraurethral origin: Skene's duct cysts, urethral or suburethral diverticulum

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FERTILIZATION AND EARLY CLEAVAGE

Reff :  Katz: Comprehensive Gynecology, 5th ed.

         In most mammals, including humans, the egg is released from the ovary in the metaphase II stage. When the egg enters the fallopian tube, it is surrounded by a cumulus of granulosa cells (cumulus oophorus) and intimately surrounded by a clear zona pellucida. Within the zona pellucida are both the egg and the first polar body. Meanwhile, spermatozoa are transported through the cervical mucus and the uterus and into the fallopian tubes. During this transport period the sperm undergo two changes: capacitation and acrosome reaction. These changes activate enzyme systems within the sperm head and make it possible for the sperm to transgress the cumulus oophorus and the zona pellucida.

       The sperm are attracted to an egg through the process known as chemotaxis, which is related to capacitation of the sperm. The process is aided by the binding of progesterone to a surface receptor on the sperm. This allows an increase in intracellular calcium ion concentration, which increases sperm motility (chemokinesis). Once the sperm has passed the barrier of the zona pellucida, it attaches to the cell membrane of the egg and enters the cytoplasm. When the sperm enters the cytoplasm, intracytoplasmic structures, the coronal granules, arrange themselves in an orderly fashion around the outermost portion of the cytoplasm just beneath the cytoplasmic membrane, and the sperm head swells and gives rise to the male pronucleus. The egg completes its second meiotic division, casting off the second polar body to a position also beneath the zona pellucida. The female pronucleus swells as well. In most mammals the male pronucleus can be recognized as the larger of the two. The pronuclei, which contain the haploid sets of chromosomes of maternal and paternal origin, do not fuse in mammals. How-ever, the nuclear membranes surrounding them disappear, and the chromosomes contained within each membrane arrange themselves on the developing spindle of the first mitotic division. In this way the diploid complement of chromosomes is reestablished, completing the process of fertilization.

         Cell division (cleavage) then occurs, giving rise to the two-cell embryo. The first division takes about 20 hours to complete, and the actual phase of fertilization generally occurs in the ampulla of the fallopian tube. A significant number of fertilized ova do not complete cleavage for a number of reasons, including failure of appropriate chromosome arrangement on the spindle, specific gene defects that prevent the formation of the spindle, and environmental factors. Importantly, teratogens acting at this point are usually either completely destructive or cause little or no effect. Twinning may occur by the separation of the two cells produced by cleavage, each of which has the potential to develop into a separate embryo. Twinning may occur at any stage until the formation of the blastula, since each cell is totipotential. Both genetic and environmental factors are probably involved in the causation of twinning.

Maternal Anatomy

Reff: Williams Obstetrics > Section II. Anatomy and Physiology > Chapter 2. Maternal Anatomy > Introduction The organs of reproduction of women are classified as either external or internal. There may be marked variation in anatomical structures in a given woman, and this is especially true for major blood vessels and nerves.

External Generative Organs The pudenda—commonly designated the vulva—includes all structures visible externally from the pubis to the perineum, that is, the mons pubis, labia majora and minora, clitoris, hymen, vestibule, urethral opening, and various glandular and vascular structures .

Mons Pubis

The mons pubis, or mons veneris, is the fat-filled cushion that lies over the symphysis pubis. After puberty, the skin of the mons pubis is covered by curly hair that forms the escutcheon. In women, it is distributed in a triangular area, the base of which is formed by the upper margin of the symphysis. In men, the escutcheon is not so well circumscribed.

Labia Majora

These structures vary somewhat in appearance, principally according to the amount of fat that is contained within the tissues. Embryologically, the labia majora are homologous with the male scrotum. The round ligaments terminate at the upper borders. After repeated childbearing, the labia majora are less prominent. They are 7 to 8 cm in length, 2 to 3 cm in width, and 1 to 1.5 cm in thickness, and are somewhat tapered at the lower extremities. In children and nulliparous women, the labia majora usually lie in close apposition, whereas in multiparous women, they may gape widely. They are continuous directly with the mons pubis above and merge into the perineum posteriorly at a site where they are joined medially to form the posterior commissure.

Before puberty, the outer surface of the labia is similar to that of the adjacent skin, but after puberty the labia are covered with hair. In nulliparous women, the inner surface is moist and resembles a mucous membrane, whereas in multiparous women, the inner surface becomes more skinlike. The labia majora are richly supplied with sebaceous glands. Beneath the skin, there is a layer of dense connective tissue that is rich in elastic fibers and adipose tissue but is nearly void of muscular elements. Unlike the squamous epithelium of the vagina and cervix, there are epithelial appendages in parts of the vulvar skin. A mass of fat beneath the skin provides the bulk of the volume of the labium, and this tissue is supplied with a rich plexus of veins.

Labia Minora

The labia minora vary greatly in size and shape. In nulliparous women, they usually are not visible behind the nonseparated labia majora. In multiparas, it is common for the labia minora to project beyond the labia majora.

Each labium minus is a thin fold of tissue that is moist and reddish, similar in appearance to a mucous membrane. The labia minora are covered by stratified squamous epithelium. Although there are no hair follicles in the labia minora, there are many sebaceous follicles and, occasionally, a few sweat glands. The interior of the labial folds is composed of connective tissue with many vessels and some smooth muscular fibers. They are supplied with a variety of nerve endings and are extremely sensitive. The tissues of the labia minora converge superiorly, where each is divided into two lamellae; the lower pair fuse to form the frenulum of the clitoris, and the upper pair merge to form the prepuce. Inferiorly, the labia minora extend to approach the midline as low ridges of tissue that fuse to form the fourchette.

Clitoris

The clitoris is the principal female erogenous organ. It is the homologue of the penis and is located near the superior extremity of the vulva. This erectile organ projects downward between the branched extremities of the labia minora. The clitoris is composed of a glans, a corpus, and two crura. The glans is made up of spindle-shaped cells, and in the body there are two corpora cavernosa, in the walls of which are smooth muscle fibers. The long, narrow crura arise from the inferior surface of the ischiopubic rami and fuse just below the middle of the pubic arch to form the corpus.

The clitoris rarely exceeds 2 cm in length. Its free end is pointed downward and inward toward the vaginal opening. The glans is usually less than 0.5 cm in diameter and is covered by stratified squamous epithelium that is richly supplied with nerve endings. The vessels of the erectile clitoris are connected with the vestibular bulbs.

There is a delicate network of free nerve endings in the labia majora, labia minora, and clitoris (Krantz, 1958). Tactile discs are found in abundance in these areas. Genital corpuscles, which are mediators of erotic sensation, vary considerably in number. These structures are abundant in the labia minora and in the skin that overlies the glans clitoris.

Vestibule

The vestibule is an almond-shaped area that is enclosed by the labia minora laterally and extends from the clitoris to the fourchette. The vestibule is the functionally mature female structure of the urogenital sinus of the embryo. In the mature state, the vestibule usually is perforated by six openings: the urethra, the vagina, the two ducts of the Bartholin glands, and, at times, the two ducts of the paraurethral glands, also called the Skene ducts and glands. The posterior portion of the vestibule between the fourchette and the vaginal opening is called the fossa navicularis, and it is usually observed only in nulliparous women

The pair of Bartholin glands are about 0.5 to 1 cm in diameter, and each is situated beneath the vestibule on either side of the vaginal opening. They are the major vestibular glands, and the ducts are 1.5 to 2 cm long and open on the sides of the vestibule just outside the lateral margin of the vaginal orifice. At times of sexual arousal, they secrete mucoid material. These glands may harbor Neisseria gonorrhoeae or other bacteria, which in turn may cause infection and a Bartholin gland abscess.

Urethral Opening

The lower two thirds of the urethra lies immediately above the anterior vaginal wall. The urethral opening or meatus is in the midline of the vestibule, 1 to 1.5 cm below the pubic arch, and a short distance above the vaginal opening. Ordinarily, the paraurethral ducts, also known as the Skene ducts, open onto the vestibule on either side of the urethra. The ducts occasionally open on the posterior wall of the urethra just inside the meatus.

Vestibular Bulbs

Embryologically, the vestibular bulbs correspond to the anlage of the corpus spongiosum of the penis. These are almond-shaped aggregations of veins, 3 to 4 cm long, 1 to 2 cm wide, and 0.5 to 1 cm thick, that lie beneath the mucous membrane on either side of the vestibule. They are in close apposition to the ischiopubic rami and are partially covered by the ischiocavernosus and constrictor vaginae muscles. The vestibular bulbs terminate interiorly at about the middle of the vaginal opening and extend upward toward the clitoris. During childbirth, they may be injured and may even rupture to form a vulvar hematoma.

Vaginal Opening and Hymen

In most virginal women, the vaginal opening most often is hidden by the overlapping labia minora. There are marked differences in shape and consistency of the hymen, which is composed mainly of elastic and collagenous connective tissue. Both the outer and inner surfaces are covered by stratified squamous epithelium. The hymen has no glandular or muscular elements, and it is not richly supplied with nerve fibers.

In the newborn, the hymen is very vascular and redundant. In pregnant women, its epithelium is thick, and the tissue is rich in glycogen. After menopause, the epithelium is thin, and focal cornification may develop. In adult women, the hymen is a membrane of various thickness that surrounds the vaginal opening more or less completely. Its aperture varies in diameter from pinpoint size to one that admits the tip of one or even two fingers.

The appearance of the hymen cannot be used to determine whether a woman has begun sexual activity. A fimbriated type of hymen in virginal women may be indistinguishable from one that has been penetrated during intercourse. As a rule, however, it is torn at several sites during first coitus, usually in the posterior portion. Identical tears may occur by other penetration, for example, tampons used during menstruation. The edges of the torn tissue soon cicatrize, and the hymen becomes divided permanently into two or more portions that are separated by narrow sulci. Occasionally with hymenal rupture, there may be profuse bleeding.

Changes produced in the hymen by childbirth are usually readily recognizable. Over time, the hymen consists of several cicatrized nodules of various sizes. Imperforate hymen is a rare lesion in which the vaginal orifice is occluded completely, causing retention of menstrual blood 

Vagina

This musculomembranous structure extends from the vulva to the uterus and is interposed anteriorly and posteriorly between the urinary bladder and the rectum . The upper portion of the vagina arises from the müllerian ducts, and the lower portion is formed from the urogenital sinus. Anteriorly, the vagina is separated from the bladder and urethra by connective tissue, often referred to as the vesicovaginal septum. Posteriorly, between the lower portion of the vagina and the rectum, there are similar tissues that together form the rectovaginal septum. The upper fourth of the vagina is separated from the rectum by the rectouterine pouch, also called the cul-de-sac of Douglas. Normally, the anterior and posterior vaginal walls lie in contact, with only a slight space intervening between the lateral margins. Vaginal length varies considerably, but commonly, the anterior and posterior vaginal walls are, respectively, 6 to 8 cm and 7 to 10 cm in length. The upper end of the vaginal vault is subdivided into the anterior, posterior, and two lateral fornices by the uterine cervix. These are of considerable clinical importance because the internal pelvic organs usually can be palpated through their thin walls. Moreover, the posterior fornix provides surgical access to the peritoneal cavity.

Prominent midline longitudinal ridges project into the vaginal lumen from the anterior and posterior walls. In nulliparous women, numerous transverse ridges, or rugae, extend outward from and almost at right angles to the longitudinal ridges. In postmenopausal multiparous women, the vaginal walls often are smooth.

The vaginal mucosa is composed of noncornified stratified squamous epithelium. Beneath the epithelium is a thin fibromuscular coat, usually consisting of an inner circular layer and an outer longitudinal layer of smooth muscle. A thin layer of connective tissue beneath the mucosa and the muscularis is rich in blood vessels. It is controversial whether this connective tissue—often referred to as perivaginal endopelvic fascia—is a definite fascial plane in the strict anatomical sense.

There are no vaginal glands. After giving birth, fragments of stratified epithelium occasionally are embedded in the vaginal connective tissue. They may form vaginal inclusion cysts, which are not true glands. In the absence of glands, the vagina is kept moist by a small amount of secretion from the cervix. During pregnancy, there is copious, acidic vaginal secretion, which normally consists of a curdlike product of exfoliated epithelium and bacteria. Lactobacillus species are also recovered in higher concentrations than in nonpregnant women (Larsen and Galask, 1980; McGregor and French, 2000).

The vagina has an abundant vascular supply. The upper third is supplied by the cervicovaginal branches of the uterine arteries, the middle third by the inferior vesical arteries, and the lower third by the middle rectal and internal pudendal arteries. The vaginal artery may branch directly from the internal iliac artery. An extensive venous plexus immediately surrounds the vagina and follows the course of the arteries. Lymphatics from the lower third of the vagina, along with those of the vulva, drain primarily into the inguinal lymph nodes. Those from the middle third drain into the internal iliac nodes, and those from the upper third drain into the iliac nodes.

Perineum

The many structures that make up the perineum. Most of the support of the perineum is provided by the pelvic and urogenital diaphragms. The pelvic diaphragm consists of the levator ani muscles plus the coccygeus muscles posteriorly. The levator ani muscles form a broad muscular sling that originates from the posterior surface of the superior pubic rami, from the inner surface of the ischial spine, and between these two sites, from the obturator fascia. Some of these muscle fibers are inserted around the vagina and rectum to form efficient functional sphincters. In a recent study utilizing magnetic resonance imaging, Tunn (2003) and Hoyte (2004) and their colleagues used magnetic-resonance imaging and reported significant variation in the levator ani muscle, endopelvic fascia, and urethral support in nulliparous women. The urogenital diaphragm is external to the pelvic diaphragm and includes the triangular area between the ischial tuberosities and the symphysis. The urogenital diaphragm is made up of the deep transverse perineal muscles, the constrictor of the urethra, and the internal and external fascial coverings.

The major blood supply to the perineum is via the internal pudendal artery and its branches. These include the inferior rectal artery and posterior labial artery. The innervation of the perineum is primarily via the pudendal nerve and its branches. The pudendal nerve originates from the S2, S3, and S4 level of the spinal cord. Perineal Body The median raphe of the levator ani, between the anus and the vagina, is reinforced by the central tendon of the perineum. The bulbocavernosus, superficial transverse perineal, and external anal sphincter muscles also converge on the central tendon. Thus, these structures contribute to the perineal body, which provides much of the support for the perineum.

Internal Generative Organs Uterus The nonpregnant uterus is situated in the pelvic cavity between the bladder anteriorly and the rectum posteriorly. Almost the entire posterior wall of the uterus is covered by serosa, or peritoneum, the lower portion of which forms the anterior boundary of the recto-uterine cul-de-sac, or pouch of Douglas. Only the upper portion of the anterior wall of the uterus is so covered. The lower portion is united to the posterior wall of the bladder by a well-defined loose layer of connective tissue.

Size and Shape

The uterus resembles a flattened pear in shape. It consists of two major but unequal parts: an upper triangular portion, the body, or corpus; and a lower, cylindrical, or fusiform portion, the cervix, which projects into the vagina. The isthmus is that portion of the uterus between the internal cervical os and the endometrial cavity. It is of special obstetrical significance because it forms the lower uterine segment during pregnancy. The oviducts, or fallopian tubes, emerge from the cornua of the uterus at the junction of the superior and lateral margins. The convex upper segment between the points of insertion of the fallopian tubes is called the fundus. The round ligaments insert below the tubes on the anterior side. They are covered by a fold of peritoneum that extends to the pelvic sidewall. These folds are called the broad ligaments, however, they do not constitute the anatomical definition of a ligament.

The prepubertal uterus varies in length from 2.5 to 3.5 cm (Orsini and colleagues, 1984). The uterus of adult nulliparous women is from 6 to 8 cm in length as compared with 9 to 10 cm in multiparous women. Uteri of nonparous women average 50 to 70 g, and those of parous women average 80 g or more (Langlois, 1970). In the premenarchal girl, the body of the uterus is only half as long as the cervix. In nulliparous women, the two are about equal in length. In multiparous women, the cervix is only a little more than a third of the total length of the organ. After menopause, uterine size decreases as a consequence of atrophy of both myometrium and endometrium.

The bulk of the body of the uterus, but not the cervix, is composed of muscle. The inner surfaces of the anterior and posterior walls lie almost in contact, and the cavity between these walls forms a mere slit. The cervical canal is fusiform and is open at each end by small apertures, the internal os and the external os.

Pregnancy-Induced Uterine Changes

Pregnancy stimulates remarkable uterine growth due to hypertrophy of muscle fibers. The weight of the uterus increases from 70 g to about 1100 g at term. Its total volume averages about 5 L. The uterine fundus, a previously flattened convexity between tubal insertions, now becomes dome shaped. The round ligaments now appear to insert at the junction of the middle and upper thirds of the organ. The fallopian tubes elongate, but the ovaries grossly appear unchanged.

Cervix

Anteriorly, the upper boundary of the cervix is the internal os, which corresponds to the level at which the peritoneum is reflected upon the bladder. The supravaginal segment is covered by peritoneum on its posterior surface. This segment is attached to the cardinal ligaments anteriorly, and it is separated from the overlying bladder by loose connective tissue. The other segment is the lower vaginal portion of the cervix, also called the portio vaginalis.

Before childbirth, the external cervical os is a small, regular, oval opening. After childbirth, the orifice is converted into a transverse slit that is divided such that there are the so-called anterior and posterior lips of the cervix. If torn deeply during delivery, it might heal in such a manner that it appears to be irregular, nodular, or stellate. These changes are sufficiently characteristic to permit an examiner to ascertain with some certainty whether a given woman has borne children by vaginal delivery.

The mucosa of the cervical canal is composed of a single layer of very high ciliated columnar epithelium that rests on a thin basement membrane. Numerous cervical glands extend from the surface of the endocervical mucosa directly into the subjacent connective tissue. These glands furnish the thick, tenacious cervical secretions. If the ducts of the cervical glands are occluded, retention cysts, known as nabothian cysts, are formed.

Body of the Uterus

The wall of the body of the uterus is composed of serosal, muscular, and mucosal layers. The serosal layer is formed by the peritoneum that covers the uterus. It is firmly adherent except at sites just above the bladder and at the lateral margins, where the peritoneum is deflected to form the broad ligaments.

Endometrium

This mucosal layer lines the uterine cavity in nonpregnant women. It is a thin, pink, velvet-like membrane that on close examination is found to be perforated by a large number of minute ostia of the uterine glands. The endometrium normally varies greatly in thickness, and measures from 0.5 mm to as much as 5 mm. It is composed of surface epithelium, glands, and interglandular mesenchymal tissue in which there are numerous blood vessels.

The epithelium of the endometrial surface is made up of a single layer of closely packed, high columnar, ciliated cells. The tubular uterine glands are invaginations of the epithelium. The glands extend through the entire thickness of the endometrium to the myometrium, which is occasionally penetrated for a short distance. Histologically, the inner glands resemble the epithelium of the surface and are lined by a single layer of columnar, partially ciliated epithelium that rests on a thin basement membrane. The glands secrete a thin, alkaline fluid. The connective tissue of the endometrium, between the surface epithelium and the myometrium, is a mesenchymal stroma. Histologically, the stroma varies remarkably throughout the ovarian cycle.

After menopause, the endometrium is atrophic and the epithelium flattens. The glands gradually disappear, and the interglandular tissue becomes more fibrous.

The vascular architecture of the uterus and the endometrium is of signal importance in pregnancy. The uterine and ovarian arteries branch and penetrate the uterine wall obliquely inward and reach its middle third. They then ramify in a plane that is parallel to the surface and are therefore named the arcuate arteries (DuBose and colleagues, 1985). Radial branches extend from the arcuate arteries at right angles and enter the endometrium to become coiled or spiral arteries. Also from the radial arteries, basal arteries branch at a sharp angle. The coiled arteries supply most of the midportion and all of the superficial third of the endometrium. The walls of these vessels are responsive (sensitive) to the action of a number of hormones, especially by vasoconstriction, and thus probably serve an important role in the mechanism(s) of menstruation. The straight basal endometrial arteries extend only into the basal layer of the endometrium and are not responsive to hormonal action.

Myometrium

The myometrium makes up the major portion of the uterus. It is composed of bundles of smooth muscle united by connective tissue in which there are many elastic fibers. According to Schwalm and Dubrauszky (1966), the number of muscle fibers of the uterus progressively diminishes caudally such that, in the cervix, muscle comprises only 10 percent of the tissue mass. In the inner wall of the body of the uterus, there is relatively more muscle than in the outer layers; and in the anterior and posterior walls, there is more muscle than in the lateral walls. During pregnancy, the upper myometrium undergoes marked hypertrophy, but there is no significant change in cervical muscle content.

Ligaments

The broad ligaments are made up of two winglike structures that extend from the lateral margins of the uterus to the pelvic walls. They divide the pelvic cavity into anterior and posterior compartments. Each broad ligament consists of a fold of peritoneum. The inner two thirds of the superior margin form the mesosalpinx, to which the fallopian tubes are attached. The outer third of the superior margin, which extends from the fimbriated end of the oviduct to the pelvic wall, forms the infundibulopelvic ligament or suspensory ligament of the ovary, through which the ovarian vessels traverse.

At the lateral margin of each broad ligament, the peritoneum is reflected onto the side of the pelvis. The thick base of the broad ligament is continuous with the connective tissue of the pelvic floor. The densest portion is usually referred to as the cardinal ligament—also called the transverse cervical ligament or the Mackenrodt ligament—and is composed of connective tissue that medially is united firmly to the supravaginal portion of the cervix.

A vertical section through the uterine end of the broad ligament is triangular, and the uterine vessels and ureter are found within its broad base. In its lower part, it is widely attached to the connective tissues that are adjacent to the cervix, that is, the parametrium. The upper part is made up of three folds that nearly cover the oviduct, the utero-ovarian ligament, and the round ligament.

The round ligaments extend from the lateral portion of the uterus, arising somewhat below and anterior to the origin of the oviducts. Each round ligament is located in a fold of peritoneum that is continuous with the broad ligament and extends outward and downward to the inguinal canal, through which it passes to terminate in the upper portion of the labium majus. In nonpregnant women, the round ligament varies from 3 to 5 mm in diameter, and is composed of smooth muscle cells. The round ligament corresponds embryologically to the gubernaculum testis of men. During pregnancy, the round ligaments undergo considerable hypertrophy and increase appreciably in both length and diameter.

Each uterosacral ligament extends from an attachment posterolaterally to the supravaginal portion of the cervix to encircle the rectum and inserts into the fascia over the sacrum. Umek and colleagues (2004) used MR-imaging to describe anatomical variations of these ligaments. The ligaments are composed of connective tissue and some smooth muscle and are covered by peritoneum. They form the lateral boundaries of the pouch of Douglas.

Blood Vessels

The vascular supply of the uterus is derived principally from the uterine and ovarian arteries. The uterine artery, a main branch of the internal iliac artery—referred to in the past as the hypogastric artery—enters the base of the broad ligament and makes its way medially to the side of the uterus. Immediately adjacent to the supravaginal portion of the cervix, the uterine artery divides. The smaller cervicovaginal artery supplies blood to the lower cervix and upper vagina. The main branch turns abruptly upward and extends as a highly convoluted vessel that traverses along the margin of the uterus. A branch of considerable size extends to the upper portion of the cervix, and numerous other branches penetrate the body of the uterus. Just before the main branch of the uterine artery reaches the oviduct, it divides into three terminal branches. The ovarian branch of the uterine artery anastomoses with the terminal branch of the ovarian artery; the tubal branch makes its way through the mesosalpinx and supplies part of the oviduct; and the fundal branch is distributed to the uppermost uterus.

About 2 cm lateral to the cervix, the uterine artery crosses over the ureter . The proximity of the uterine artery and vein to the ureter at this point is of great surgical significance. Because of their close proximity, the ureter may be injured or ligated during a hysterectomy when the vessels are clamped and ligated.

The ovarian artery is a direct branch of the aorta. It enters the broad ligament through the infundibulopelvic ligament. At the ovarian hilum, it divides into a number of smaller branches that enter the ovary. Its main stem, however, traverses the entire length of the broad ligament very near the mesosalpinx and makes its way to the upper lateral portion of the uterus. Here it anastomoses with the ovarian branch of the uterine artery. There are numerous additional communications among the arteries on both sides of the uterus.

When the uterus is in a contracted state, its numerous venous lumens are collapsed, however, in injected specimens the greater part of the uterine wall appears to be occupied by dilated venous sinuses. On either side, the arcuate veins unite to form the uterine vein, which empties into the internal iliac vein and thence into the common iliac vein. Some of the blood from the upper uterus, the ovary, and the upper part of the broad ligament is collected by several veins. Within the broad ligament, these veins form the large pampiniform plexus that terminates in the ovarian vein. The right ovarian vein empties into the vena cava, whereas the left ovarian vein empties into the left renal vein. During pregnancy, there is marked hypertrophy of the blood supply to the uterus.

Lymphatics

The endometrium is abundantly supplied with true lymphatic vessels that are confined largely to the basal layer. The lymphatics of the underlying myometrium are increased in number toward the serosal surface and form an abundant lymphatic plexus just beneath it. Lymphatics from the cervix terminate mainly in the hypogastric nodes, which are situated near the bifurcation of the common iliac vessels. The lymphatics from the body of the uterus are distributed to two groups of nodes. One set of vessels drains into the internal iliac nodes. The other set, after joining certain lymphatics from the ovarian region, terminates in the periaortic lymph nodes.

Innervation

The nerve supply to the pelvic area is derived principally from the sympathetic nervous system, but also partly from the cerebrospinal and parasympathetic systems. The parasympathetic system is represented on either side by the pelvic nerve, which is made up of a few fibers that are derived from the second, third, and fourth sacral nerves. It loses its identity in the cervical ganglion of Frankenhäuser. The sympathetic system enters the pelvis by way of the internal iliac plexus that arises from the aortic plexus just below the promontory of the sacrum. After descending on either side, it also enters the uterovaginal plexus of Frankenhäuser, which is made up of ganglia of various sizes, but particularly of a large ganglionic plate that is situated on either side of the cervix and just above the posterior fornix in front of the rectum.

Branches from these plexuses supply the uterus, bladder, and upper vagina. In the 11th and 12th thoracic nerve roots, there are sensory fibers from the uterus that transmit the painful stimuli of contractions to the central nervous system. The sensory nerves from the cervix and upper part of the birth canal pass through the pelvic nerves to the second, third, and fourth sacral nerves, whereas those from the lower portion of the birth canal pass primarily through the pudendal nerve. Knowledge of the innervation of dermatomes and its clinical application to providing epidural or spinal analgesia for labor and vaginal or cesarean delivery.

Oviducts

More commonly called the fallopian tubes, the oviducts vary in length from 8 to 14 cm. They are covered by peritoneum, and their lumen is lined by mucous membrane. Each tube is divided into an interstitial portion, isthmus, ampulla, and infundibulum. The interstitial portion is embodied within the muscular wall of the uterus. The isthmus, or the narrow portion of the tube that adjoins the uterus, passes gradually into the wider, lateral portion, or ampulla. The infundibulum, or fimbriated extremity, is the funnel-shaped opening of the distal end of the fallopian tube. The oviduct varies considerably in thickness; the narrowest portion of the isthmus measures from 2 to 3 mm in diameter, and the widest portion of the ampulla measures from 5 to 8 mm. The fimbriated end of the infundibulum opens into the abdominal cavity. One projection, the fimbria ovarica, which is considerably longer than the other fimbriae, forms a shallow gutter that approaches or reaches the ovary.

The musculature of the fallopian tube is arranged in an inner circular and an outer longitudinal layer. In the distal portion, the two layers are less distinct and, near the fimbriated extremity, are replaced by an interlacing network of muscular fibers. The tubal musculature undergoes rhythmic contractions constantly, the rate of which varies with the hormonal changes of the ovarian cycle. The greatest frequency and intensity of contractions is reached during transport of ova.

The oviducts are lined by a single layer of columnar cells, some of them ciliated and others secretory. The ciliated cells are most abundant at the fimbriated extremity, elsewhere, they are found in discrete patches. There are differences in the proportions of these two types of cells in different phases of the ovarian cycle. Because there is no submucosa, the epithelium is in close contact with the underlying muscle. In the tubal mucosa, there are cyclical histological changes similar to those of the endometrium, but much less striking. The mucosa is arranged in longitudinal folds that are more complex toward the fimbriated end. On cross sections through the uterine portion, four simple folds are found that form a figure that resembles a Maltese cross. The isthmus has a more complex pattern. In the ampulla, the lumen is occupied almost completely by the arborescent mucosa, which consists of very complicated folds. The current produced by the tubal cilia is such that the direction of flow is toward the uterine cavity. Tubal peristalsis is believed to be an extraordinarily important factor in transport of the ovum.

The tubes are supplied richly with elastic tissue, blood vessels, and lymphatics. Sympathetic innervation of the tubes is extensive, in contrast to their parasympathetic innervation.

Diverticula may extend occasionally from the lumen of the tube for a variable distance into the muscular wall and reach almost to the serosa. 

Embryological Development of the Uterus and Oviducts

The uterus and tubes arise from the müllerian ducts, which first appear near the upper pole of the urogenital ridge in the fifth week of embryonic development. This ridge is composed of the mesonephros, gonad, and associated ducts. The first indication of the development of the müllerian duct is a thickening of the coelomic epithelium at about the level of the fourth thoracic segment. This thickening becomes the fimbriated extremity of the fallopian tube, which invaginates and grows caudally to form a slender tube at the lateral edge of the urogenital ridge. In the sixth week of embryonic life, the growing tips of the two müllerian ducts approach each other in the midline; they reach the urogenital sinus 1 week later. At that time, a fusion of the two müllerian ducts to form a single canal is begun at the level of the inguinal crest, that is, the gubernaculum (primordium of the round ligament). Thus, the upper ends of the müllerian ducts produce the oviducts and the fused parts give rise to the uterus. The vaginal canal is not patent throughout its entire length until the sixth month of fetal life (Koff, 1933). Because of the clinical importance of anomalies that arise from abnormal fusion and dysgenesis of these structures.

Ovaries

Compared with each other, as well as between women, the ovaries vary considerably in size. During childbearing years, they are from 2.5 to 5 cm in length, 1.5 to 3 cm in breadth, and 0.6 to 1.5 cm in thickness. After menopause, ovarian size diminishes remarkably. The position of the ovaries also varies, but they usually are situated in the upper part of the pelvic cavity and rest in a slight depression on the lateral wall of the pelvis between the divergent external and internal iliac vessels—the ovarian fossa of Waldeyer. The ovary is attached to the broad ligament by the mesovarium. The utero-ovarian ligament extends from the lateral and posterior portion of the uterus, just beneath the tubal insertion, to the uterine pole of the ovary. Usually, it is several centimeters long and 3 to 4 mm in diameter. It is covered by peritoneum and is made up of muscle and connective tissue fibers. The infundibulopelvic or suspensory ligament of the ovary extends from the upper or tubal pole to the pelvic wall; through it course the ovarian vessels and nerves.

In young women, the exterior surface of the ovary is smooth, with a dull white surface through which glisten several small, clear follicles. As the woman ages, the ovaries become more corrugated, and in elderly women, the exterior surfaces may be convoluted markedly.

The ovary consists of two portions, the cortex and medulla. The cortex is the outer layer, which varies in thickness with age and becomes thinner with advancing years. It is in this layer that the ova and graafian follicles are located. The cortex is composed of spindle-shaped connective tissue cells and fibers, among which are scattered primordial and graafian follicles in various stages of development. As the woman ages, the follicles become less numerous. The outermost portion of the cortex, which is dull and whitish, is designated the tunica albuginea. On its surface, there is a single layer of cuboidal epithelium, the germinal epithelium of Waldeyer.

The medulla is the central portion, which is composed of loose connective tissue that is continuous with that of the mesovarium. There are a large number of arteries and veins in the medulla and a small number of smooth muscle fibers that are continuous with those in the suspensory ligament.

The ovaries are supplied with both sympathetic and parasympathetic nerves. The sympathetic nerves are derived primarily from the ovarian plexus that accompanies the ovarian vessels. Others are derived from the plexus that surrounds the ovarian branch of the uterine artery. The ovary is richly supplied with nonmyelinated nerve fibers, which for the most part accompany the blood vessels. These are merely vascular nerves, whereas others form wreaths around normal and atretic follicles, and these give off many minute branches that have been traced up to, but not through, the membrana granulosa.

Embryology

The earliest sign of a gonad is one that appears on the ventral surface of the embryonic kidney at a site between the eighth thoracic and fourth lumbar segments at about 4 weeks. The coelomic epithelium is thickened, and clumps of cells are seen to bud off into the underlying mesenchyme. This circumscribed area of the coelomic epithelium is called the germinal epithelium. By the fourth to sixth week, however, there are many large ameboid cells in this region that have migrated into the body of the embryo from the yolk sac. These primordial germ cells are distinguishable by their large size and certain morphological and cytochemical features.

When the primordial germ cells reach the genital area, some enter the germinal epithelium and others mingle with the groups of cells that proliferate from it or lie in the mesenchyme. By the end of the fifth week, rapid division of all these types of cells results in development of a prominent genital ridge. The ridge projects into the body cavity medially to a fold in which there are the mesonephric (wolffian) and the müllerian ducts. By the seventh week, it is separated from the mesonephros except at the narrow central zone, the future hilum, where the blood vessels enter. At this time, the sexes can be distinguished, because the testes can be recognized by well-defined radiating strands of cells (sex cords). These cords are separated from the germinal epithelium by mesenchyme that is to become the tunica albuginea. The sex cords, which consist of large germ cells and smaller epithelioid cells derived from the germinal epithelium, develop into the seminiferous tubules and tubuli rete. The latter establishes connection with the mesonephric tubules that develop into the epididymis. The mesonephric ducts become the vas deferens.

In the female embryo, the germinal epithelium continues to proliferate for a much longer time. The groups of cells thus formed lie at first in the region of the hilum. As connective tissue develops between them, these appear as sex cords. These cords give rise to the medullary cords and persist for variable times (Forbes, 1942). By the third month, medulla and cortex are defined (see Fig. 2–15). The bulk of the organ is made up of cortex, a mass of crowded germ and epithelioid cells that show some signs of grouping, but there are no distinct cords as in the testis. Strands of cells extend from the germinal epithelium into the cortical mass, and mitoses are numerous. The rapid succession of mitoses soon reduces the size of the germ cells to the extent that these no longer are differentiated clearly from the neighboring cells. These germ cells are now called oogonia.

By the fourth month, some germ cells in the medullary region begin to enlarge. These are called primary oocytes at the beginning of the phase of growth that continues until maturity is reached. During this period of cell growth, many oocytes undergo degeneration, both before and after birth. A single layer of flattened follicular cells that were derived originally from the germinal epithelium soon surrounds the primary oocytes. These structures are now called primordial follicles and are seen first in the medulla and later in the cortex. Some follicles begin to grow even before birth, and some are believed to persist in the cortex almost unchanged until menopause.

By 8 months, the ovary has become a long, narrow, lobulated structure that is attached to the body wall along the line of the hilum by the mesovarium, in which lies the epoöphoron. The germinal epithelium has been separated for the most part from the cortex by a band of connective tissue—tunica albuginea—which is absent in many small areas where strands of cells, usually referred to as cords of Pflüger, are in contact with the germinal epithelium. Among these cords are cells believed by many investigators to be oogonia that have come to resemble the other epithelial cells as a result of repeated mitoses. In the underlying cortex, there are two distinct zones. Superficially, there are nests of germ cells in synapsis, interspersed with Pflüger cords and strands of connective tissue. In the deeper zone, there are many groups of germ cells in synapsis, as well as primary oocytes, prospective follicular cells, and a few primordial follicles.

At term, the various types of ovarian cells in the human female fetus may still be found.

Histology

From the first stages of its development until after the menopause, the ovary undergoes constant change. The number of oocytes at the onset of puberty has been estimated variously at 200,000 to 400,000. Because only one ovum ordinarily is cast off during each ovarian cycle, it is evident that a few hundred ova suffice for purposes of reproduction.

The glandular elements of ovaries of adult women include interstitial, thecal, and luteal cells. The interstitial glandular elements are formed from cells of the theca interna of degenerating or atretic follicles; the thecal glandular cells are formed from the theca interna of ripening follicles; and the true luteal cells are derived from the granulosa cells of ovulated follicles and from the undifferentiated stroma that surround them.

The huge store of primordial follicles at birth is exhausted gradually after sexual maturation and through the reproductive span. Block (1952) found that there is a gradual decline from a mean of 439,000 oocytes in girls younger than 15 years to a mean of 34,000 in women older than 36 years. In young girls, the greater portion of the ovary is composed of the cortex, which is filled with large numbers of closely packed primordial follicles. In young women, the cortex is relatively thinner but still contains a large number of primordial follicles. Each primordial follicle is made up of an oocyte and its surrounding single layer of epithelial cells, which are small and flattened, spindle-shaped, and somewhat sharply differentiated from the still smaller and spindly cells of the surrounding stroma.

The oocyte is a large, spherical cell in which there is clear cytoplasm and a relatively large nucleus located near the center of the ovum. In the nucleus, there are one large and several smaller nucleoli, and numerous masses of chromatin. 

Embryological Remnants

There are a number of vestigial wolffian structures that are identified after embryogenesis of the female reproductive system. Some of these occasionally cause clinical concerns. The parovarium can be found in the scant loose connective tissue within the broad ligament in the vicinity of the mesosalpinx. It comprises a number of narrow vertical tubules that are lined by ciliated epithelium. These tubules connect at the upper ends with a longitudinal duct that extends just below the oviduct to the lateral margin of the uterus, where it ends blindly near the internal os. This canal is the remnant of the wolffian (mesonephric) duct in women and is called the Gartner duct. The parovarium, also a remnant of the wolffian duct, is homologous embryologically with the caput epididymis in men. The cranial portion of the parovarium is the epoöphoron, or organ of Rosenmüller; the caudal portion, or paroöphoron, is a group of vestigial mesonephric tubules that lie in or around the broad ligament. It is homologous embryologically with the paradidymis of men. The paroöphoron in adult women usually disappears.

Pelvic Anatomy

The false pelvis lies above the linea terminalis and the true pelvis below this anatomical boundary.The false pelvis is bounded posteriorly by the lumbar vertebra and laterally by the iliac fossa. In front, the boundary is formed by the lower portion of the anterior abdominal wall.

The true pelvis is the portion important in childbearing. It is bounded above by the promontory and alae of the sacrum, the linea terminalis, and the upper margins of the pubic bones, and below by the pelvic outlet. The cavity of the true pelvis can be described as an obliquely truncated, bent cylinder with its greatest height posteriorly. Its anterior wall at the symphysis pubis measures about 5 cm, and its posterior wall, about 10 cm.

The walls of the true pelvis are partly bony and partly ligamentous. The posterior boundary is the anterior surface of the sacrum, and the lateral limits are formed by the inner surface of the ischial bones and the sacrosciatic notches and ligaments. In front, the true pelvis is bounded by the pubic bones, the ascending superior rami of the ischial bones, and the obturator foramen.

The sidewalls of the true pelvis of an adult woman converge somewhat. Extending from the middle of the posterior margin of each ischium are the ischial spines. These are of great obstetrical importance because the distance between them usually represents the shortest diameter of the pelvic cavity. They also serve as valuable landmarks in assessing the level to which the presenting part of the fetus has descended into the true pelvis. The sacrum forms the posterior wall of the pelvic cavity. Its upper anterior margin corresponds to the promontory that may be felt during bimanual pelvic examination in women with a small pelvis. It can provide a landmark for clinical pelvimetry. Normally the sacrum has a marked vertical and a less pronounced horizontal concavity, which in abnormal pelves may undergo important variations. A straight line drawn from the promontory to the tip of the sacrum usually measures 10 cm, whereas the distance along the concavity averages 12 cm.

The descending inferior rami of the pubic bones unite at an angle of 90 to 100 degrees to form a rounded arch under which the fetal head must pass.

Pelvic Joints

Symphysis Pubis

Anteriorly, the pelvic bones are joined together by the symphysis pubis. This structure consists of fibrocartilage and the superior and inferior pubic ligaments; the latter are frequently designated the arcuate ligament of the pubis.

Sacroiliac Joints

Posteriorly, the pelvic bones are joined by the articulations between the sacrum and the iliac portion of the innominate bones to form the sacroiliac joints. These joints also have a certain degree of mobility.

Relaxation of the Pelvic Joints

During pregnancy, relaxation of these joints likely results from hormonal changes. Abramson and co-workers (1934) observed that relaxation of the symphysis pubis commenced in women in the first half of pregnancy and increased during the last 3 months. They also observed that this laxity began to regress immediately after parturition and that regression was completed within 3 to 5 months. The symphysis pubis also increases in width during pregnancy—more so in multiparas than in primigravidas—and returns to normal soon after delivery.

There are important changes in sacroiliac joint mobility. Borell and Fernstrom (1957) demonstrated that the rather marked mobility of the pelvis at term was caused by an upward gliding movement of the sacroiliac joint. The displacement, which is greatest in the dorsal lithotomy position, may increase the diameter of the outlet by 1.5 to 2.0 cm. This is the main justification for placing a woman in this position for a vaginal delivery. The increase in the diameter of the pelvic outlet, however, occurs only if the sacrum is allowed to rotate posteriorly, that is, only if the sacrum is not forced anteriorly by the weight of the maternal pelvis against the delivery table or bed (Russell, 1969, 1982). Sacroiliac joint mobility is also the likely reason that the McRoberts maneuver often is successful in releasing an obstructed shoulder in a case of shoulder dystocia (see Chap. 20, Shoulder Dystocia). These changes have also been attributed to the success of the modified squatting position to hasten second-stage labor (Gardosi and co-workers, 1989). The squatting position may increase the interspinous diameter and the diameter of the pelvic outlet (Russell, 1969, 1982). These latter observations are unconfirmed, but this position is assumed for birth in many primitive societies.

Planes and Diameters of the Pelvis

The pelvis is described as having four imaginary planes.

1.      The plane of the pelvic inlet—the superior strait.

2.      The plane of the pelvic outlet—the inferior strait.

3.      The plane of the midpelvis—the least pelvic dimensions.

4.      The plane of greatest pelvic dimension—of no obstetrical significance.

Pelvic Inlet

The pelvic inlet (superior strait) is bounded posteriorly by the promontory and alae of the sacrum, laterally by the linea terminalis, and anteriorly by the horizontal pubic rami and the symphysis pubis. The inlet of the female pelvis typically is more nearly round than ovoid. Caldwell and co-workers (1934) identified radiographically a nearly round or gynecoid pelvic inlet in approximately 50 percent of white women.

Four diameters of the pelvic inlet are usually described: anteroposterior, transverse, and two obliques. The obstetrically important anteroposterior diameter is the shortest distance between the promontory of the sacrum and the symphysis pubis, and is designated the obstetrical conjugate. Normally, this measures 10 cm or more.

The transverse diameter is constructed at right angles to the obstetrical conjugate and represents the greatest distance between the linea terminalis on either side. It usually intersects the obstetrical conjugate at a point about 4 cm in front of the promontory. The segment of the obstetrical conjugate from the intersection of these two lines to the promontory is designated the posterior sagittal diameter of the inlet.

Each of the two oblique diameters extends from one of the sacroiliac synchondroses to the iliopectineal eminence on the opposite side. They average less than 13 cm.

The anteroposterior diameter of the pelvic inlet that has been identified as the true conjugate does not represent the shortest distance between the promontory of the sacrum and the symphysis pubis. The shortest distance is the obstetrical conjugate, which is the shortest anteroposterior diameter through which the head must pass in descending through the pelvic inlet. Obstetrical conjugate cannot be measured directly with the examining fingers. For clinical purposes, the obstetrical conjugate is estimated indirectly by subtracting 1.5 to 2 cm from the diagonal conjugate. The latter is determined by measuring the distance from the lower margin of the symphysis to the promontory of the sacrum.

Midpelvis

The midpelvis is measured at the level of the ischial spines—the midplane, or plane of least pelvic dimensions. It is of particular importance following engagement of the fetal head in obstructed labor. The interspinous diameter, 10 cm or somewhat more, is usually the smallest diameter of the pelvis. The anteroposterior diameter through the level of the ischial spines normally measures at least 11.5 cm. Its posterior component (posterior sagittal diameter), between the sacrum and the line created by the interspinous diameter, is usually at least 4.5 cm.

Pelvic Outlet

The pelvic outlet consists of two approximately triangular areas that are not in the same plane. They have a common base, which is a line drawn between the two ischial tuberosities . The apex of the posterior triangle is at the tip of the sacrum, and the lateral boundaries are the sacrosciatic ligaments and the ischial tuberosities. The anterior triangle is formed by the area under the pubic arch. Three diameters of the pelvic outlet usually are described: the anteroposterior, transverse, and posterior sagittal.

Pelvic Shapes

In the past, x-ray pelvimetry was used frequently in women with suspected cephalopelvic disproportion or fetal malpresentation. Caldwell and Moloy (1933, 1934) developed a classification of the pelvis that is still used. The classification is based on the shape of the pelvis, and its familiarity helps the clinician understand better the mechanisms of labor.

The Caldwell–Moloy classification is based on measurement of the greatest transverse diameter of the inlet and its division into anterior and posterior segments. The shapes of these are used to classify the pelvis as gynecoid, anthropoid, android, or platypelloid. The character of the posterior segment determines the type of pelvis, and the character of the anterior segment determines the tendency. These are both determined because many pelves are not pure but are mixed types; for example, a gynecoid pelvis with an android tendency means that the posterior pelvis is gynecoid and the anterior pelvis is android in shape.

From viewing the four basic types, the configuration of the gynecoid pelvis would intuitively seem suited for delivery of most fetuses. Indeed, Caldwell and co-workers (1939) reported that the gynecoid pelvis was found in almost 50 percent of women. In contrast, in the android pelvis, the posterior sagittal diameter at the inlet is much shorter than the anterior sagittal diameter, limiting the use of the posterior space by the fetal head. Moreover, the anterior portion is narrow and triangular. The extreme android pelvis presages a poor prognosis for vaginal delivery. In the anthropoid pelvis, the anteroposterior diameter of the inlet is greater than the transverse. This results in an oval anteroposteriorly, with the anterior segment somewhat narrow and pointed. Variations of anthropoid-type pelves are found in about one third of women. The platypelloid pelvis has a flattened gynecoid shape with short anteroposterior and wide transverse diameters. Pure varieties are found in fewer than 3 percent of women.

Pelvic Size and Its Clinical Estimation

Pelvic Inlet Measurements

In many abnormal pelves, the anteroposterior diameter of the pelvic inlet—the obstetrical conjugate—is considerably shortened. The diagonal conjugate is clinically estimated by measuring the distance from the sacral promontory to the lower margin of the symphysis pubis. Two fingers of the dominant hand are introduced into the vagina. The mobility of the coccyx is first evaluated. The anterior surface of the sacrum is next palpated from below upward and its vertical and lateral curvatures noted. In normal pelves, only the last three sacral vertebrae can be felt without indenting the perineum. Conversely, in markedly contracted pelves, the entire anterior surface of the sacrum usually is readily palpable. Next, in order to reach the sacral promontory, the examiner's elbow must be flexed and the perineum forcibly indented by the knuckles of the third and fourth fingers. The index and the second fingers are carried up and over the anterior surface of the sacrum. By deeply inserting the wrist, the promontory may be felt by the tip of the second finger as a projecting bony margin. With the finger closely applied to the most prominent portion of the upper sacrum, the vaginal hand is elevated until it contacts the pubic arch. The immediately adjacent point on the index finger is marked. The distance between the mark and the tip of the second finger is the diagonal conjugate. The obstetrical conjugate is computed by subtracting 1.5 to 2.0 cm, depending on the height and inclination of the symphysis pubis. If the diagonal conjugate is greater than 11.5 cm, it is justifiable to assume that the pelvic inlet is of adequate size for vaginal delivery of a normal-sized fetus.

Engagement

Descent of the biparietal plane of the fetal head to a level below that of the pelvic inlet is termed engagement. When the biparietal—the largest—diameter of the normally flexed fetal head has passed through the inlet, the head is engaged. Although engagement usually is regarded as a phenomenon of labor, in nulliparas it may occur during the last few weeks of pregnancy. When it does so, it is confirmatory evidence that the pelvic inlet is adequate for that fetal head. With engagement, the fetal head serves as an internal pelvimeter to demonstrate that the pelvic inlet is ample for that fetus.

Engagement is ascertained by vaginal examination or by abdominal palpation. With vaginal examination, the station of the lowermost part of the fetal head in relation to the level of the ischial spines is determined. If the lowest part of the occiput is at or below the level of the spines, the head usually, but not always, is engaged. The distance from the plane of the pelvic inlet to the level of the ischial spines is approximately 5 cm in most pelves. Although the distance from the biparietal plane of the unmolded fetal head to the vertex is usually only 3 to 4 cm, accurate determination of engagement may be difficult if there is considerable elongation of the fetal head from molding or formation of a caput succedaneum.

Abdominal examination is a less satisfactory method to determine engagement. If the biparietal plane of a term-sized infant has descended through the inlet, the examining fingers cannot reach the lowermost part of the head. Thus, when pushed downward over the lower abdomen, the examining fingers will slide over that portion of the head proximal to the biparietal plane (nape of the neck) and diverge. Conversely, if the head is not engaged, the examining fingers can easily palpate the lower part of the head and will converge.

Fixation of the fetal head occurs when descent proceeds to a depth that prevents its free movement when pushed right and then left by both hands placed over the lower abdomen. Fixation is not necessarily synonymous with engagement. Although a head that is freely movable on abdominal examination cannot be engaged, fixation of the head is sometimes seen when the biparietal plane is still 1 cm or more above the pelvic inlet, especially if the head is molded appreciably.

Pelvic Outlet Measurements

An important dimension of the pelvic outlet that is accessible for clinical measurement is the diameter between the ischial tuberosities, variously called the biischial diameter, intertuberous diameter, and transverse diameter of the outlet. A measurement of more than 8 cm is considered normal. The measurement of the transverse diameter of the outlet can be estimated by placing a closed fist against the perineum between the ischial tuberosities. Usually the closed fist is wider than 8 cm. The shape of the subpubic arch also can be evaluated at the same time by palpating the pubic rami from the subpubic region toward the ischial tuberosities.

Midpelvis Estimation

Clinical estimation of midpelvic capacity by any direct form of measurement is not possible. If the ischial spines are quite prominent, the sidewalls are felt to converge, and the concavity of the sacrum is very shallow, then suspicion of a contraction is aroused.