Two hearts, one rhythm: monochorionic diamniotic twins

Monochorionic diamniotic (MCDA) twins are a unique type of twin pregnancy because they have separate amniotic sacs but share a single placenta. Typically, this occurs when a single zygote (blastocyst) separates at approximately 4–8 days after development, the result is an MCDA pregnancy. These foetuses have two yolk sacs, two amniotic sacs, and one chorionic sac in common. A trophoblast has already developed at this point, producing a single placenta. The twins are referred to as "identical" by laypeople. In actuality, they share the same gender and are phenotypically similar. It mostly accounts for about 20–30% of twin pregnancies. There are benefits and drawbacks related to MCDA twins.