Small Uterine Cavity Deformation: Bicornuate or Myomatous Uterus

GENESIS

Several different types of uterine problems can limit the size and/or shape of the uterine cavity and thus enhance the likelihood of fetal deformation. Embryonic development of the female reproductive tract results from the fusion of Müllerian ducts and urogenital sinus. Müllerian ducts differentiate to form the uterus, fallopian tubes, cervix, and upper one-third of the vagina. Examples include a malformed uterus caused by failure of the Müllerian ducts to completely fuse during embryogenesis, resulting in either symmetric or asymmetric structural anomalies of the uterus such as didelphic uterus with duplicated cervix, bicornuate uterus, septate uterus, and arcuate uterus ( Fig. 45.1 ). Uterine defects can be subgrouped into arcuate uteri, canalization defects (septate and subseptate uteri), and unification defects (unicornuate, bicornuate, and didelphys uteri) ( Fig. 45.2 ). Women with a didelphic or completely septate uterus and two external uterine orifices had a significantly higher rate of cesarean delivery (91% vs. 18%) than a control group of 5763 women with normal uterine morphology. Women with a bicornuate or incomplete septate uterus and one external uterine orifice had significantly higher rates of preterm birth (27% vs. 5%) and placental abruption (14% vs. 0.7%) than the control group.

Estimates of the frequency of anomalous Müllerian development vary widely based on the mode of ascertainment. Among 101 women who had routine hysterosalpingography (HSG) and 3D transvaginal sonography as part of an infertility evaluation, 6 normal uteri and 30 congenital uterine anomalies were diagnosed (3 arcuate, 1 unicornuate, 4 bicornuate, 2 didelphys, and 20 septate uteri). Congenital anomalies were correctly identified in 30 of 30 cases by 3D transvaginal sonography, but in only 10 of 30 cases by HSG. Only 7 of the 20 septi would have been surgically corrected if patients only had HSG, and 3D transvaginal sonography provided better evaluation of uterine anomalies with lower cost and morbidity.

Methodologic biases affect frequency estimates because reproductive tracts are more commonly investigated in women with miscarriage and infertility, and anomalies are more prevalent in women with these problems. The most accurate diagnostic procedures are combined HSG, laparoscopy, and 3D ultrasonography. The prevalence of congenital uterine anomalies is approximately 6.7% in the general population, approximately 7.3% in the infertile population, and approximately 16.7% in the recurrent miscarriage population. The arcuate uterus is the most common anomaly in the general and recurrent miscarriage population. In contrast, the septate uterus is the most common anomaly in the infertile population. A systematic review of nine different studies comprising 3805 women evaluated the association between different types of congenital uterine anomalies and various reproductive outcomes. Metaanalysis showed that arcuate uteri were associated with increased rates of second-trimester miscarriage and fetal malpresentation at delivery. Canalization defects reduced fertility and increased rates of miscarriage and preterm delivery. Unification defects were associated with increased rates of preterm birth and fetal malpresentation. Arcuate uteri were specifically associated with second-trimester miscarriage. All uterine anomalies increase the chance of fetal malpresentation at delivery, thereby increasing the risk of craniofacial deformations and positional orthopedic defects. Among 316 women with congenital uterine malformations, 15.3% had incompetence of the cervix, so preterm delivery can result from an incompetent cervix and the malformation of the uterus. Uterine rupture has also been reported, resulting in an abdominal pregnancy. Unicornuate uterus with a rudimentary horn has a high incidence of obstetric and gynecological complications. Ruptured ectopic pregnancy in the rudimentary horn is one of the most dreaded complications that can have grave consequences for both mother and fetus.

It is estimated that at least 1% to 2% of women have a clinically significant malformation of the uterus, and the general risk of a deformation problem for a fetus in a malformed uterus is about 30%. Such deformations can include craniofacial deformations, overlapping sutures, joint contractures, limb deformations or disruptions, edema and/or grooves, and thoracic constriction resulting in pulmonary hypoplasia. This would imply that 3 to 6 infants per 1000 may have a deformation problem secondary to gestation within a malformed uterus. Vascular disruption within the fetal limb can also occur with severe uterine constriction. Among 556 twin pregnancies, 3.1% had a known uterine anomaly (9 septate uterus, 3 bicornuate, 3 arcuate, 1 unicornuate, and 1 didelphys). In patients with twin pregnancies, the presence of a uterine anomaly was associated with an increased risk of cerclage, preterm birth, and lower birth weights, but not fetal growth restriction.

Uterine fibroids (leiomyomas) are benign tumors that become clinically apparent in many women of reproductive age. In pregnancy, many are incidentally diagnosed, and if they are large, they often require careful monitoring concerning their size, number, and location. They present with a variety of symptoms including excessive menstrual bleeding, dysmenorrhea and intermenstrual bleeding, chronic pelvic pain, and pressure symptoms such as a sensation of bloatedness, increased urinary frequency, and bowel disturbance. In addition, they may affect reproductive functions, contributing to subfertility, early pregnancy loss, and later pregnancy complications. Myomectomy for submucosal fibroids greater than 2 cm and for intramural fibroids distorting the endometrial contour can improve fertility. Submucosal fibroid location and distortion of the endometrial cavity (either submucosal or deeply infiltrating intramural fibroids) are most likely to impair fertility and warrant surgical removal. Nowadays, with advanced preparations, myomectomies during cesarean section are safely and frequently performed when the benefits outweigh the risks. Women with prenatal exposure to diethylstilbestrol (DES) have a slightly higher incidence of fibroids compared with unexposed women. The risk is strongest for women exposed to DES in the first trimester, corresponding to early stages of fetal Müllerian development. Rarely, a large uterine fibroid can also result in fetal deformation and/or disruption, and sometimes a small fibroma will enlarge rapidly under the influence of increased levels of estrogen during late gestation. Among 121 women with 179 pregnancies and fibroids 4 cm or greater in size on ultrasonography at the dating scan, the size (4–7 cm, 7–10 cm, >10 cm), number (multiple/single), location (lower uterus/body of uterus), and type (intramural, combination of intramural/subserosal, subserosal) were ascertained. Preterm delivery was more likely in those with multiple fibroids compared with single fibroids (18% vs. 6%). There was a higher cesarean section rate for fibroids in the lower part of uterus than in the body of the uterus, as well as a higher rate of postpartum hemorrhage and increased estimated blood loss. Increasing size of fibroid was associated with greater rates of hemorrhage, increased estimated blood loss, and higher rates of admission for fibroid-related pain. Women with multiple rather than large fibroids have a significantly increased risk of preterm birth and cesarean delivery, whereas large fibroids are associated with a higher risk of premature rupture of membranes. There is one case report of arthrogryposis associated with the presence of a “giant” uterine fibroid. When joint contractures result from space limitations within the uterus, the most common etiology is oligohydramnios, but similar constraint can occur with large fibroids.