In twins, how many yolk sacs are there in relation to the number of amniotic sacs?

The correct answer reflects that in twin pregnancies, the number of yolk sacs typically equals the number of amniotic sacs. In a twin pregnancy, whether both are identical (monozygotic) or fraternal (dizygotic), each embryo generally develops its own yolk sac and amniotic sac.

In monozygotic twins, the zygote can split at different stages, which might result in the formation of varying numbers of amniotic cavities (for example, they may share a single amniotic sac if division occurs early). However, in cases where they each have their own separate sacs, each will have its own yolk sac as well.

In the case of dizygotic twins, each twin will develop individually with one yolk sac and one amniotic sac. This attachment ensures that the embryos receive appropriate nourishment from their respective yolk sacs while developing within the amniotic fluid in their distinct amniotic sacs.

Thus, the number of yolk sacs aligns with the number of amniotic sacs in both types of twin pregnancies under normal circumstances. This understanding is essential for assessing twin gestations through ultrasound or during early prenatal evaluations.