jus-tified to others in terms of widely recognized ethical principles.
7. Reevaluate the decision after it is acted on. Repeat the evalu-ation of the major options in light of informevalu-ation gained during the implementation of the decision. Was the best possible decision made? What lessons can be learned from the discussion and resolution of the problem?
SUGGESTED READINGS
American College of Obstetricians and Gynecologists. Ethical deci-sion making in obstetrics and gynecology. ACOG Committee Opinion No. 390. Obstet Gynecol. 2007;110(6):1479–1487.
American College of Obstetricians and Gynecologists. Innovative practice: ethical guidelines. ACOG Committee Opinion No. 352.
Obstet Gynecol. 2006;108(6):1589–1595.
American College of Obstetricians and Gynecologists. Maternal decision making, ethics, and the law. ACOG Committee Opinion No. 321. Obstet Gynecol. 2005;106(5):1127–1137.
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4 Embryology and Anatomy
An understanding of reproductive anatomy and its developmental precursors is important for learners in their ability to apply basic diagnostic and therapeutic principles in patient care.
29 tal anomalies. For example, the genetic disease congen-ital adrenal hyperplasia (CAH) causes a decreased production of cortisol that results in a compensatory increase in androgens. The genitalia of female fetuses with CAH are ambiguous, that is, neither normal female nor normal male.
Development of the Ovary
Ovaries are homologous to the testes in the male. Both types of gonads begin development as gonadal or genital ridges that form during the 5th week of gestation from the urogenital ridges. Fingerlike bands of epithelial cells pro-ject from the surface of the gonad into each gonadal ridge, forming irregularly shaped primary sex cords. Growth of these cords into the gonadal ridge results in the creation of an outer cortex and an inner medulla in the indifferent gonad.
Primordial germ cells that give rise to gametes appear in the wall of the yolk sac (now called the umbilical vesicle) during the 3rd week of development (see Fig. 4.1). From this location, primordial germ cells migrate along the allantois in the connecting stalk to the dorsal mesentery of the hindgut and then into the gonadal ridges, where they become associated with the primary sex cords by the 6th week. In the female, the primordial germ cells become oogonia, which divide by mitosis during fetal life; no oogonia are formed after birth. If the primordial germ cells fail to migrate to the genital ridges, the ovary does not develop.
By approximately the 10th week of development, the undifferentiated gonad has developed into an identifi-able ovary. Primary sex cords degenerate, and secondary sex cords or cortical cords appear. These cords extend from the surface epithelium into the underlying mesenchyme (Fig. 4.2, right column of figure). By approximately 16 weeks nowledge of the embryology and anatomy of the
female genital system is helpful in understanding both normal anatomy and the congenital anom-alies that occur. Embryology may be useful in many areas of gynecologic and obstetric practice. For example, in gynecologic oncology, embryology can assist clinicians in predicting the growth and routes of spread of gynecologic cancers; in urogynecology and pelvic reconstructive surgery, it can enhance a surgeon’s comprehension of the compo-nents of pelvic support and possible defects. It can also play a key role in understanding and diagnosing various aspects of sexual dysfunction.
The ovaries, fallopian tubes, uterus, and upper portion of the vagina are derived from the intermediate mesoderm, while the external genitalia develop from genital swellings in the pelvic region. Beginning in the 4th week (postfertil-ization) of development, the intermediate mesoderm forms the urogenital ridges along the posterior body wall. As their name implies, these ridges contribute to the forma-tion of the urinary and genital systems (Fig. 4.1).
The gonads, genital ducts, and external genitalia all pass through an indifferent (undifferentiated) stage in which it is not possible to determine sex based on the appearance of these struc-tures. The genetic sex of an embryo is determined by the sex chromosome (X or Y) carried by the sperm that fertilizes the oocyte. The Y chromosome contains a gene called SRY (sex-determining region on Y) that encodes a protein called testis-determining factor (TDF). When this pro-tein is present, the embryo develops male sex characteris-tics. The ovary-determining gene is WNT4; when this gene is present and SRY is absent, the embryo develops female characteristics. Gonads become structurally male or female by the 7th week of development, and external genitalia become dif-ferentiated by the 12th week. The influence of androgens is crucial in the normal development of the external geni-talia. Any condition that increases the level of androgen production in a female embryo will cause
developmen-K
of gestation, cortical cords in the ovary organize into primordial follicles. Each follicle eventually consists of an oogonium, derived from a primary germ cell, sur-rounded by a single layer of squamous follicular cells, derived from the cortical cords. Follicular maturation begins when the oogonia enter the first stage of meiotic division (at which point they are called primary oocytes).
Oocyte development is then arrested until puberty, when one or more follicles are stimulated to continue development each month (see Chapter 34, Puberty).
In male embryos, the primary sex cords do not degen-erate; instead, they develop into seminiferous (or testis) cords that eventually give rise to the rete testis and semi-niferous tubules (see Fig. 4.2, left column of figure). A layer of dense connective tissue (the tunica albuginea) separates the seminiferous cords from the surface epithe-lium, which eventually becomes the testis. Cortical cords do not form in the male embryo.
As they develop, gonads descend from their starting point high up in the primitive body cavity, where they are attached to a mesenchymal condensation called the gubernaculum. Ovaries move caudally to a location just below the rim of the true pelvis immediately adjacent to the fimbriated end of the fallopian tubes. The testis, on the other hand, continues to descend, eventually migrating through the anterior abdominal wall just superior to the inguinal ligament. The gubernaculum in the female fetus eventually forms the ovarian and round ligaments (see Fig. 4.2 and Fig. 4.3).
Development of the Genital Ducts
In both male and female embryos, two pairs of ducts develop—the mesonephric (wolffian) and parameso-nephric (müllerian) ducts. As with the gonad, these ducts pass through an indifferent stage in which both pairs of ducts are pres-ent in both the male and the female embryo. Differpres-entiation of the female ductal system is not dependent on development of the ovaries (Fig. 4.4).
In the male embryo, the mesonephric ducts, which drain the embryonic mesonephric kidneys, eventually form the epididymis, ductus deferens, and ejaculatory ducts. In the female embryo, the mesonephric ducts disappear. The para-mesonephric ducts persist to form major parts of the female reproductive tract (the fallopian tubes, uterus, and upper por-tion of the vagina). Paramesonephric ducts begin as invagi-nations of the epithelium covering the urogenital ridges, eventually forming longitudinally oriented tubes. The cranial end of each duct opens into the body (future peri-toneal) cavity. The ducts grow caudally until the two cau-dal ends contact the posterior wall of the urogenital sinus.
This contact induces the posterior wall to proliferate and form the vaginal plate that eventually gives rise to the lower portion of the vagina. Meanwhile, the lower ends of the paramesonephric ducts fuse to form the upper portion
Wolffian duct
Excretory mesonephric tubule
Glomerulus
Aorta
Genital ridge 4 weeks
6 weeks Mesonephric ridge
Mesonephric duct
Paramesonephric duct
Primary sex cords
Proliferative coelomic epithelium
Dorsal mesentery (B)
(A)
(C) Cloaca
Hindgut Genital ridge
Urogenital ridge
Mesonephros
Primordial germ cells
3 weeks Allantois
FIGURE 4.1. Early development of the urogenital system.
(A) Beginning at approximately 3 weeks of gestation, uro-genital ridges arise along the posterior wall of the coelomic cavity. Primordial germ cells migrate across the allantois into the genital ridges. (B) and (C) These transverse sections through the lumbar region of the human embryo show development of the indifferent gonad from the genital ridges at 4 weeks and 6 weeks of gestation. (Modified from Sadler TW. Langman’s Medical Embryology. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:240–241.
Rete testis
Abdominal ostium of the uterine duct
Developing primordial follicles
Fimbriae
Epoophoron Paroophoron
Round ligament of uterus
Gartner’s cyst Testis cords
Testis cord Tunica albuginea
Mesonephric duct
Rete testis
Rete testis Seminiferous cords
Seminiferous vesicle
Ductus deferens
Epididymis Tunica albuginea
Mesonephric duct Mesonephric duct
MALE FEMALE
FEMALE
MALE
Degenerating primary sex cords
Cortical cords of the ovary
Mesonephros
Paramesonephric duct
Paramesonephric tubercle Paramesonephric
tubercle Uterovaginal
canal
Suspensory ligament of ovary
Ovarian ligament Mesovarium
Corpus uteri
Cervix
Vagina
(A) (B)
(C) 8 weeks (D) Birth
(E) 16 weeks (F) Birth
FIGURE 4.2. Development of the gonads and their migration to their adult locations. At approximately 6 weeks of gestation, the gonads have differentiated into either male or female (A and B). In female embryos, the paramesonephric ducts develop into the uterus, uterine tubes, and part of the vagina (C and D). In male embryos, the mesonephric ducts develop into the main genital tracts (ductus deferens) (E and F). (Modified from Sadler TW. Langman’s Medical Embryology. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:243 and 245.)
(A) 2 months
(C) Mature Internal oblique muscle External oblique aponeurosis
Deep inguinal ring Round ligament of uterus
Labia majora
(B) 15 weeks Primordial
ovaries
Para-mesonephric duct Developing kidney Mesonephric duct
Labia majora Round ligament of uterus Ovarian ligament
Deep inguinal ring Superficial inguinal ring Ovary
Ureter Kidney Upper
gubernaculum (inguinal fold–
becomes ovarian ligament) Lower gubernaculum (becomes round ligament of uterus)
Anterior views
FIGURE 4.3. Route of the migrating gonads in a female embryo. (A) At 2 months, the early gonads are located high up in the coelomic cavity attached to the gubernaculum. (B) The gubernaculum migrates through the anterior abdominal wall just above the inguinal ligament; this process also takes place in the male embryo. (C) The ovaries arrest their descent in the ovarian fossa, immediately subjacent to the uterus on either side. (From Moore KL, Dalley AF. Clinically Oriented Anatomy. 5th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:Fig. 2.14.)
of the vagina, cervix, and uterus. The cranial portion of each duct remains separated and forms the fallopian tube on each side. As the ducts move toward fusion in the mid-line, they carry a fold of peritoneum with them that becomes the broad ligament.
Development of the External Genitalia
The cloaca is formed from a dilatation of the caudal end of the hindgut and is covered exteriorly by the cloacal mem-brane. Eventually, the cloaca is separated into the
urogeni-tal sinus anteriorly and the anorecurogeni-tal canal posteriorly by the urorectal septum. This septum forms from a collec-tion of mesoderm in the pelvic floor that grows downward during the 5th to the 8th weeks of gestation to reach the cloacal membrane. At the same time, the genital tuber-cle develops at the cranial end of the cloacal membrane, while labioscrotal swellings and urogenital folds appear on each side (Fig. 4.5A). The genital tubercle enlarges in both the male and the female (Fig. 4.5B). In the presence of estrogens and the absence of androgens, external genitalia are feminized. The genital tubercle develops into the
cli-Fallopian tube
Vaginal plate
Cervix
Fornix
Vagina
Hymen Uterine septum
Urogenital sinus
Caudal tip of paramesonephric
ducts
(A)
(B)
(C)
Caudal tip of paramesonephric
ducts
toris (Fig. 4.5C). The unfused urogenital folds form the labia minora, and the labioscrotal swellings become the labia majora (Fig. 4.5D).
At approximately 15 weeks of gestation, transverse ultra-sonography can distinguish between the two sexes, although it is not definitive.
ANATOMY Bony Pelvis
The bony pelvis is composed of the paired innominate bones and the sacrum. The innominate bones are joined anteriorly to form the symphysis pubis, and each is artic-ulated posteriorly with the sacrum through the sacroiliac joint (Fig. 4.6). The sacrum is composed of five or six sacral vertebrae, which are fused in adulthood. The sacrum articulates with the coccyx inferiorly and with the fifth lumbar vertebra superiorly.
The pelvis is divided into the greater pelvis (false pelvis) and the lesser pelvis (true pelvis), which are sep-arated by the linea terminalis. The greater pelvis distributes the weight of the abdominal organs and supports the preg-nant uterus at term. The greater pelvis is bounded by the lumbar vertebrae posteriorly, an iliac fossa bilaterally, and the abdominal wall anteriorly. The true pelvis contains the pelvic viscera including the uterus, vagina, bladder, fallopian tubes, ovaries, and the distal rectum and anus. It is formed by the sacrum and coccyx posteriorly and by the ischium and pubis laterally and anteriorly.
In obstetrics, it is important to assess the size of the pelvis to determine whether it is of adequate capacity for vaginal birth.
This evaluation is based on the diameters of the pelvic outlet, pelvic inlet, and midpelvis. Measurement of these diameters is called pelvimetry and can be made radiograph-ically, with computed tomography (the most accurate method), or during a pelvic examination. One of the most important measurements is that of the obstetrical conju-gate (Fig. 4.7), which is the narrowest fixed distance through which the fetal head must pass during a vaginal delivery.
FIGURE 4.4. Development of the internal reproductive organs from the müllerian ducts in the female embryo.
(A) Initially, the ducts are separate structures that begin to fuse lengthwise at their caudal ends. (B) This fusion creates the lumen of the uterus. Simultaneously, the vagina devel-ops where the urogenital sinus meets the müllerian ducts, the vaginal plate. (C) Eventually, the uterus, cervix and vagina are formed. (Modified from Sadler TW. Langman’s Medical Embryology. 10th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006:246.)
The obstetric conjugate cannot be measured directly due to the presence of the bladder.
It is calculated indirectly by measuring the diagonal conjugate, which is the distance between the lower bor-der of the pubis anteriorly to the lower sacrum at the level of the ischial spines. The obstetric conjugate is 1.5 to 2 cm shorter. In general, it should be 11.0 cm or greater to accommodate a fetal head of normal size. Other measure-ments include the interspinous diameter (the distance between the ischial spines) and transverse diameter (the distance measured at the greatest width of the superior aperture).
Clitoris
Anus Anus
Anus Urogenital folds
Urogenital sinus Urogenital folds (labia minora)
Labia minora Hymen Vaginal orifice Urogenital orifice Labioscrotal swellings
Genital tubercle Genital tubercle
Urogenital folds
Labioscrotal swellings (labia majora)
Labia majora Glans clitoris
Scrotal raphe Scrotum Urethral groove Glans penis
Labia minora Hymen Vaginal orifice Urogenital orifice
Labia majora Glans clitoris (A)
FEMALE MALE
7 weeks
10 weeks
12 weeks
Near term (B)
(C)
(D)
Anus
Urethral groove Urogenital folds Labioscrotal swellings (scrotal folds)
Labioscrotal swellings (scrotal folds)
Scrotum Scrotal raphe Urethral raphe Urethral orifice Glans penis FIGURE 4.5. Comparison of the
development of male and female external genitalia. (A) Early in gestation, the genital tubercle develops along with labioscrotal swellings and urogenital folds.
(B) Shortly thereafter, the genital tubercle enlarges in both the male and female embryo. (C) The posterior commissure forms, effectively dividing genitals from anus. (D) Without the influence of a Y chromosome, the phallus regresses in relative size to form the clitoris.
Anterior longitudinal lig.
Transverse process
of L5 vertebra Iliolumbar ligs.
Anterior sacroiliac lig.
Anterior inferior iliac spine
Anterior sacrococcygeal lig.
Pubic symphysis
Ilio femoral lig.
Pubofemoral lig.
Sacroiliac joint
Obturator membrane Head of femur (joint capsule removed)
Sacrotuberous and sacrospinous ligs.
Anterior superior iliac spine
Posterior superior iliac spine
Iliac crest
Iliac crest
Ala of sacrum Sacral promontory
Anterior superior iliac spine Sacrum
Coccyx Acetabulum Pubic tubercle Subpubic angle
Pubic arch
Pubic symphysis
Greater (false) pelvis Lesser (true) pelvis Greater
pelvis
Iliac fossa
Ilium Pubis Ischium Ala
Hip bone
(A) (B)
FIGURE 4.6. The bony pelvis. (A) Anterior view of the pelvis; the greater and lesser pelves are color-coded.
(B) The pelvic ligaments shown in detail. (From Moore, KL and Dalley AF. Clinically Oriented Anatomy. 5th ed.
Baltimore, MD: Lippincott Williams & Wilkins; 2006: Figs. 3.3B and 3.2A.)
Oblique diameter
Obstetrical conjugate
>10 cm Interspinous distance, 10 cm Transverse diameter, 13.5 cm (A) Superior view
(B) Medial view (from left) Sacral promontory Anatomical conjugate
True (obstetric) conjugate Diagonal conjugate Pubic symphysis
Plane of least pelvic dimension
Obstetric conjugate (11.5 cm)
(C) Medial view (from right)
Diagonal conjugate (13 cm) Distance measured after hand is withdrawn (11.5 cm)
FIGURE 4.7. Pelvic diameters and estimating the obstetric conjugate. (A) Superior view of the pelvis showing the diameters that are measured in pelvimetry. (B) Medial view of the pelvis demon-strating the diagonal conjugate and the obstetrical conjugate. (C) Measurement of the obstetri-cal conjugate. The examiner palpates the sacral promontory with the tip of the middle finger. The distance between the tip of the index finger, which is 1.5 cm shorter than the middle finger, and the place on the hand where the pubic symphysis is felt is measured to yield the obstetri-cal conjugate, which should be at least 11 cm. (From Moore KL, Dalley AF. Cliniobstetri-cally Oriented Anatomy. 5th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006: Fig. B3.2.)
The female pelvis may be classified into four basic types, according to the scheme of Caldwell and Moloy (Fig. 4.8), although an individual may have a pelvis that is a mixture of types. The most common type is the gynecoid pelvis, occurring in approximately 40% to 50% of women. In general, this pelvic shape is cylindrical and has adequate space along its length and breadth. The anthropoid type occurs in approximately 25% of all women, and the android pelvis occurs in approximately 20%. The platypelloid pelvis occurs in only 2% to 5% of women.
Vulva and Perineum
The perineum comprises the area of the surface of the trunk between the thighs and the buttocks, extending from the coccyx to the pubis. Anatomists also use the term “perineum” to refer to the shallow compartment that lies deep to this area and inferior to the pelvic diaphragm.
The vulva contains the labia majora, labia minora, mons pubis, clitoris, vestibule, and ducts of glands that open into the vestibule (Fig. 4.9). The labia majora are folds of skin with underlying adipose tissue, fused anteriorly with the mons pubis and posteriorly at the perineum. The skin of the labia majora contains hair follicles as well as seba-ceous and sweat glands. The labia minora are narrow skin folds lying inside the labia majora. The labia minora merge anteriorly with the prepuce and frenulum of the clitoris, and posteriorly with the labia majora and the perineum. The labia minora contain sebaceous and sweat glands, but no hair follicles, and there is no underlying adipose tissue. The clitoris, which is located anterior to the labia minora, is the embryologic homolog of the penis. It consists of two crura (corresponding to the corpora cavernosa in the male) and the glans, which is found superior to the point of fusion of the crura. On the ventral surface of the glans is the frenu-lum, the fused junction of the labia minora. The vestibule
“Round”
Gynecoid
Android
“Wedge”
“Oval”
Platypelloid
Anthropoid
“Oval-long”
FIGURE 4.8. Caldwell-Moloy pelvic types.
Mons pubis Glans of clitoris Frenulum of clitoris Labia minora Vestibule of vagina Site of perineal body
External urethral orifice
Labia majora Vaginal orifice
Anus
FIGURE 4.9. External female genitalia.
Bulbocavernosus muscle
Ischiocavernosus muscle
Vestibular bulb Bartholin’s gland Clitoris
FIGURE 4.10. The urogenital diaphragm with the skin and subcutaneous fat cut away. The musculature, blood supply, and nerve supply constitute the external part of the pelvic floor.
lies between the labia minora and is bounded anteriorly by the clitoris and posteriorly by the perineum. The urethra and the vagina open into the vestibule in the midline.
The ducts of Skene (paraurethral) glands and Bartholin glands also empty into the vestibule. Secretions from the Bartholin glands are responsible for sexually stimulated vaginal lubrication.
The muscles of the vulva (superficial transverse per-ineal, bulbocavernosus, and ischiocavernosus) lie superficial to the fascia of the urogenital diaphragm (Fig. 4.10). The vulva rests on the triangular-shaped urogenital diaphragm, which lies in the anterior part of the pelvis between the ischiopubic rami.
The Vagina
The lumen of the vagina is lined by a stratified squamous epithelium and surrounded by three layers of smooth mus-cle. Beneath the smooth muscle layers is a submucosal layer of connective tissue containing a rich supply of veins and lymphatic vessels. In children and young women, the ante-rior and poster walls of the vagina are in contact due to the presence of submucosal rugae. Because the vagina is collapsed, it appears H-shaped in cross section. The underlying rugae connect to the tendinous arch of the pelvic fascia, which is the major support of the walls of the vagina and help maintain its normal architecture. With age and childbirth, the connection between the vaginal walls and the muscu-lar pelvis may weaken or deteriorate, weakening the pelvic floor and causing the surrounding structures (bladder, rec-tum, urethra, and uterus) to become less stable.
The cervix joins the vagina at an angle between 45° and 90°. The area around the cervix, the fornix, is divided into four regions: the anterior fornix, two lateral fornices, and the posterior fornix. The posterior fornix is in close proximity to the peritoneum that forms the floor of the posterior pelvic cul-de-sac (pouch of Douglas). The cer-vical opening to the vagina, the external os, is round to oval in women who have not had children, but is often a transverse slit after childbirth. The portion of the cervix that projects into the vagina is covered with stratified squa-mous epithelium, which resembles the vaginal epithelium.
The squamous epithelium changes to a simple columnar epithelium in the transition (transformation) zone.
This zone is found at about the level of the external cervi-cal os, although it is found higher in the endocervicervi-cal canal in postmenopausal women (the histology of the cervix is discussed in more detail in Chapter 43, Cervical Neoplasia and Carcinoma).
At its lower end, the vagina traverses the urogenital diaphragm and is then surrounded by the two bulbocaver-nosus muscles of the vulva. These muscles act as a sphincter.
The hymen, a fold of mucosal-covered connective tissue, somewhat obscures the external vaginal orifice. The hymen is fragmented into irregular remnants with sexual activity and childbearing. The major blood supply to the vagina is from the vaginal artery, a branch of the hypogastric artery, also known as the internal iliac and parallel veins.
Uterus and Pelvic Support
The uterus lies between the rectum and the bladder (Fig. 4.11). Various pelvic ligaments help support the uterus and other pelvic organs. The broad ligament overlies the structures and connective tissue immediately adjacent to the uterus. Because it contains the uterine arteries and veins and the ureters, it is important to identify the broad ligament during surgery. The infundibulopelvic lig-ament connects the ovary to the posterior abdominal
wall and is composed mainly of the ovarian vessels. The uterosacral ligament connects the uterus at the level of the cervix to the sacrum and is therefore its primary support.
The cardinal ligament is attached to the side of the uterus immediately inferior to the uterine artery. The sacro-spinous ligament connects the sacrum to the iliac spine and is not attached to the uterus. This ligament is frequently used surgically to support the pelvic viscera.
The two major portions of the uterus are the cervix and the body (corpus), which are separated by a narrower isthmus. The length of the cervix is established at puberty.
Before puberty, the relative lengths of the body of the uterus and cervix are approximately equal; after puberty, under the influence of increased estrogen levels, the ratio of the body to the cervix changes to between 2:1 and 3:1.
The part of the body where the two uterine tubes enter it is called the cornu. The part of the corpus above the cornu is referred to as the fundus. In a woman who has had no children, the uterus is approximately 7 to 8 cm long and 4 to 5 cm wide at the widest part. The cervix is relatively cylindrical in shape and is 2 to 3 cm long. The body is gen-erally pear-shaped, with the anterior surface flat and the posterior surface convex. In cross section, the lumen of the uterine body is triangular.
The wall of the uterus consists of three layers:
(1) The inner mucosa, or endometrium, consists of sim-ple columnar epithelium with underlying connective tissue, which changes in structure during the men-strual cycle.
(2) The middle layer, or myometrium, consists of smooth muscle. This layer becomes greatly distensible during pregnancy; during labor, the smooth muscle in this layer contracts in response to hormonal stimulation.
(3) The outermost layer, or perimetrium, consists of a thin layer of connective tissue. It is distinct from the para-metrium, a subserous extension of the uterus between the layers of the broad ligament.
The position of the uterus can vary depending on the rela-tionship of a straight axis that extends from the cervix to the uterine fundus to the horizontal. When a woman is in the dorsal lithotomy position, the uterus may be bent forward (anteversion, AV), slightly forward but functionally straight (mid-position, MP), or bent backward (retroversion, RV).
The top of the uterus can also fold forward (anteflexion, AF) or backward (retroflexion, RF). Five combinations of these configurations are possible (Fig. 4.12). The posi-tion of the uterus is clinically important. For example, estimation of gestational age in the late part of the first trimester may be difficult when the uterus is in the RVRF or RV positions. Risk of uterine perforation during pro-cedures such as dilatation & curettage or insertion of an intrauterine device is increased in a woman with a retro-flexed or anteretro-flexed uterus. Applying traction on the cervix to pull the uterine canal into a straight line can greatly reduce this risk.
