When you hear you are having twins, many questions may come to mind: How often are twins born? What different kind of twins are there? What are monozygotic twins? What are dizygotic twins? How many twins share the same placenta? Do all identical twins have one placenta?

The process of conception does not always stop at one baby. A pregnancy with more than one fetus at one time is referred to as a multiple pregnancy. With the increase in the use of fertility drugs, multiple pregnancies have been growing in number in recent years. Twins can occur when one fertilized egg splits or when two eggs are fertilized by separate sperm.

Dizygotic twins/trizygotic triplets (fraternal or non-identical) are created when a female releases more than one egg or ovulates two or three times and all eggs are fertilized. Monozygotic (maternal/identical) twins or triplets are created if one egg is released, only one sperm fertilizes the egg, and the egg splits into multiple embryos.

This quiz was created by Dr. Amos Grunebaum to help you find out how much you know about twins!