A New Type of Twins Is Discovered: Semi-Identical Twins

The Journal of Human Genetics recently reported on a rare type of twins, who have been dubbed “semi-identical twins.” In this case, a single egg was fertilized by two sperm simultaneously, and then the egg split into twins. One of the twins was born as a “true hermaphrodite,” which means that the child had both ovarian and testicular tissue. (She’s being raised as a female.) The other child is a male. Both children are otherwise normal mentally and physically, and are now three years old.

This condition differs from “polar body twins,” which occurs when a single egg splits, and then each egg is fertilized by two different sperm. This is not the same as “semi-identical twinning” (described above), in which fertilization occurs before the egg splits.

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About Susan Heim

Susan M. Heim is an author and editor, specializing in multiples, parenting, women’s and Christian issues. Her books include "Boosting Your Baby's Brain Power"; "Chicken Soup for the Soul: Twins and More"; "It’s Twins! Parent-to-Parent Advice from Infancy Through Adolescence"; "Twice the Love: Stories of Inspiration for Families with Twins, Multiples and Singletons"; and, "Oh, Baby! 7 Ways a Baby Will Change Your Life the First Year." Upcoming books include "Chicken Soup for the Soul: All in the Family," "Chicken Soup for the Soul: Devotional Stories for Women," and "Moms of Multiples' Devotions to Go." Susan's articles and essays have appeared in many books, magazines and Web sites. She is a member of the National Association of Women Writers and the Southeastern Writers Association, and has a degree in Business Administration from Michigan State University. Susan lives with her husband and four sons (two teenagers and twin grade-schoolers) in Florida.