Sonography: dizygotic twin survival in early pregnancy.

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 conceptus. We conclude that the presence of one embryo does not affect the development of its twin.