Dr. Esra Kirsever, Gynaecologist and Obstetrician, Istanbul, Turkey
Twin-to-twin transfusion syndrome Overview
Most pregnancies result in one baby. In about one in 80 pregnancies, twins are conceived. This can occur in one of two ways:
The more common way (which accounts for two-thirds of cases) is for the two different sperm to fertilize two different eggs, resulting in what is called a dizygotic (DZ) twin gestation.
These twins are often called fraternal twins. In this type of twinning each twin has its own sac of amniotic fluid and its own placenta (afterbirth). Dizygotic twins have two sets of membranes surrounding their amniotic fluid sacs (one inner amnion layer and one outer chorion layer), and therefore they are known as diamniotic, dichorionic.
These twins are often referred to as identical twins since they have the same genetic material. Approximately one-third of MZ twins look just like fraternal twins on prenatal ultrasound since there are two separate amniotic sacs and t...