In some cases, pregnancy is complicated by preexisting abnormalities of the reproductive tract. Most of these are developmental anomalies formed during embryogenesis, but they may be acquired during adulthood and sometimes during pregnancy.
Due to abnormal embryogenesis, a number of sporadic genitourinary defects may occur. Serious defects are hazardous for the fetus and mother. Even minor maternal defects may result in an increased incidence of miscarriage, preterm labor, and abnormal fetal presentation.
Embryogenesis of the Reproductive Tract
To understand the etiology of developmental abnormalities of the vagina, cervix, and uterus, it is important to first understand their embryogenesis. This is discussed in further detail in Chapter 4, Development of Genitalia and summarized in Figure 40-1. The proper temporal sequence of gene expression and appropriate spatial relationships of developing tissues are crucial to normal development.
Development of the female reproductive systems from the genital ducts and urogenital sinus. Vestigial structures are also shown. A. Reproductive system at 6 weeks before differentiation. B. In the female, the müllerian (paramesonephric) ducts grow downward and extend to enter the urogenital sinus, after which they become fused. C. Uterine cavitation occurs at site of fused müllerian ducts and the uterus continues downward growth. D. Cavitation is complete and the lower segment and cervix, along with the upper vagina, are formed. (Reprinted from Schorge J, Schaffer J, Halvorson L, et al: Williams Gynecology, p. 403. Copyright © 2008 The McGraw-Hill Companies, Inc.)
Development of the reproductive organs from intermediate mesodermal elements begins between the third and fifth gestational weeks. Differentiation of the urinary system begins as the mesonephric ducts emerge and connect with the cloaca. Between the fourth and fifth weeks, two ureteric buds develop from the mesonephric (Wolffian) ducts and begin to grow cephalad toward the mesonephros. As each bud lengthens, it induces differentiation of the metanephros, which will become the kidney. The genital system begins development when the müllerian (paramesonephric) ducts form bilaterally between the developing gonad and the mesonephros. The müllerian ducts extend downward and laterally to the mesonephric ducts. They finally turn medially to meet and fuse together in the midline. The fused müllerian duct descends to the urogenital sinus to join the müllerian tubercle behind the cloaca. The close association between the müllerian and mesonephric ducts has clinical relevance. damage to either duct system is often associated with anomalies that involve the uterine horn, kidney, and ureter.
The uterus is formed by the union of the two müllerian ducts at about the 10th week. Fusion begins in the middle and ...