Understanding Fraternal Twins

Only about 3% of live births in the United States are twins. Among them, around 70% are fraternal twins, which result from the fertilization of two separate eggs by two different sperm. Unlike identical twins, fraternal twins share half of their genetic makeup and can have different biological sexes. “Fraternal twins are more common in pregnancies conceived with assisted reproduction,” said Sasha Andrews, M.D., a maternal-fetal medicine specialist at Obstetrix® of Colorado, part of Pediatrix® Medical Group. Additionally, “as maternal age and/or the number of children increases, so does the chance of fraternal twins.”

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