A monochorionic pregnancy is a multiple pregnancy, most commonly a twin pregnancy, in which babies are dependent on a single, shared placenta. Approximately 30% of twin pregnancies in the UK are monochorionic. Monochorionic placentation can also occur in higher-order multiple Monochorionic-monoamniotic twins are identical twins who share both a placenta and an amniotic sac. Monochorionic-diamniotic twins are identical twins who share a placenta but not an amniotic sac. ... This occurs in approximately 30 percent of pregnancies of identical twins It is most often conducted between 16 to 26 weeks of pregnancy. Studies show an 80 to 85 percent survival rate for at least one twin following laser ablation and an overall twin survival rate of 65 to 70 percent. Monochorionic twins occur in 0.3% of all pregnancies. 75% of monozygotic twin pregnancies are monochorionic; the remaining 25% are dichorionic diamniotic