Fraternal twins: Learn about the different types

Learn about the different types of twins, including fraternal twins, which are conceived from two separate eggs and sperm. Find out about rare subtypes, such as mirror twins, conjoined twins, and semi-identical twins. Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, and supporting structures. Identical, or monozygotic, twins may or may not share the same amniotic sac, depending on how early the single fertilized egg divides into 2. Fraternal twins are two babies who develop from two different eggs and sperm. Learn about their common traits, how they differ from identical twins, and what to expect during your twin pregnancy. But most twins – about 70% – are actually fraternal. Like any siblings, they may share a few traits (hair color, eye color, even personality quirks) – or they may look and act completely different. Here's how fraternal twins form, what sets them apart from identical twins, and what to expect if you're pregnant with twins.