With the application of ovulation inducing drugs and the development of in vitro fertilization, the incidence of multiple pregnancies has significantly increased compared to before. Research has found that the perinatal mortality rate of multiple pregnancies is significantly higher than that of singleton pregnancies (about 5 times), mainly due to premature birth and related complications. Among them, chorionic and amniotic are closely related to pregnancy prognosis. So, what does pregnancy mean by 'twin wool and twin sheep'?
Pregnant twin sheep usually have double chorionic and double sheep membranous sacs, which are usually formed by the division of a fertilized egg to form a twin pregnancy called monozygotic twin. Monozygotic twins generally account for about 30% of twin pregnancies, and there is currently no clear reason for how this situation occurs. If a fertilized egg divides to form two fetuses, which may have the same genetic makeup, then these two fetuses may be identical in terms of gender, blood type, appearance, and so on.
This situation usually occurs within three days after the fertilized egg, forming two independent embryos and two amniotic sacs. And there will be two layers of chorionic villi and two layers of amniotic membrane between the two amniotic sacs. This type is not prone to twin transfusion syndrome, fetal growth restriction, etc., and is relatively the most ideal type in monozygotic twins.
The earlier the gestational sac, the clearer it can show two separate gestational sacs. As pregnancy progresses, after 7-8 weeks, the gestational sac becomes larger and closer to each other, and the highly echogenic chorionic ring thickens at the bottom decidua, gradually forming the placenta; The remaining part gradually becomes thinner and eventually forms a smooth chorion.
