Why is a vanishing twin not seen in an early ultrasound?

Answer by  Ali41 (1593)

A vanishing twin often appears normal at the beginning and eventually hits a developmental roadblock. This may be while early on there is no way to tell it will vanish.

Answer by  Rose (6804)

The main reason a vanishing twin would not be seen in an early utrasounds would be that it had already vanished.

Answer by  Startwearinggreen (340)

Because sometimes they hide behind the other baby. Also when they listen to the heartbeat the beat together so they can not establish two heart beats instead of one. Its an amazing thing but also frustrating when you find there is one instead of two. I guess it's hard to tell at first.

Answer by  medhits (160)

It may have already started, or never even formed much past the point of a gestation sac. It's hard to see an embryo that wont grow, in a sac.