Chorionic twins are a type of twin pregnancy where each twin has its own chorion, the outer membrane that surrounds the fetus. This condition typically occurs in dizygotic (fraternal) twins, where two separate eggs are fertilized by two different sperm. Each twin develops in its own amniotic sac, providing individual environments for growth. In some cases, monozygotic (identical) twins can also be chorionic if the fertilized egg splits early enough to form two separate chorions. Chorionic twins are generally associated with a lower risk of complications compared to monozygotic twins that share a chorion, as they have separate placentas and amniotic sacs.