Irregular Yolk Sac Shape

OBJECTIVES: The yolk sac is the first conceptional structure that becomes sonographically visible within the gestational sac. Because the yolk sac is the primary route of exchange between the embryo and the mother, it is essential in early embryonic life. This study aimed to determine whether an irregular yolk sac shape is associated with an increased risk of spontaneous abortion. METHODS: The shape and size of the yolk sac were assessed by transvaginal sonography in 183 women who had normal and healthy pregnancies with gestational ages of 6 to 8 weeks. RESULTS: Most of the embryos had a yolk sac with a regular shape (152 of 183 [83%]), whereas the remaining embryos had a yolk sac with an irregular shape (31 of 183 [17%]). Although there was a trend toward a lower rate of irregular yolk sacs with advancing gestational age, the difference was not statistically significant (P = .13). Spontaneous abortion occurred in 6 of 183 pregnancies (3.3%): 1 of the 31 (3.2%) with an irregular yolk sac shape and 5 of the 152 (3.3%) with a regular yolk sac shape. The rates of spontaneous abortion were statistically similar for pregnancies with a regular yolk sac shape and those with an irregular shape (P > .99). CONCLUSIONS: This study suggests that an irregular yolk sac shape is unrelated to an increased risk of spontaneous abortion.