Dizygotic twin survival in early pregnancy

摘要

It has been suggested that losses of twin conceptuses in very early pregnancy are high, and that for every liveborn twin pair there are a further 10-12 twin pregnancies that end up as a singleton birth. Here we show that in a group of women who had double-ovulated and conceived, the probability of the second egg also becoming fertilized and developing is 20-30% - which is comparable to the probability of conception and survival of a single conceptus2. We conclude that the presence of one embryo does not affect the development of its twin. So far, no direct measure has been available of the proportion of double ovulations that lead to twins. We have obtained this information by using ultrasound to identify pregnant women with two corpora lutea, and correlating these with the number who had one or two fetuses (dizygotic twins) in early pregnancy. The corpus luteum is an endocrine organ that develops in the ovary at the site at which the egg was released, and can therefore act as an indicator of the number of ovulation events.