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Twinning is Sometimes a Family Affair

Posted: March 23rd, 2009 | Author: Editor | Filed under: parenting, pregnancy, women's health | Tags: , , , , , , , , , , , , | No Comments »

   Statistics vary but about one in every ninety births in the United States are twins, and sometimes the propensity to have twins can run in families. There are two main types of twins, identical and fraternal. Identical twins occur when a single fertilized egg splits in two, usually before the eighth day of development. Each then develops into two separate but genetically identical embryos. Heredity and family history seem to play no role in the occurrence of identical twins.  

Identical twins do not run in families, but fraternal twins do.

   There does seem to be a genetic link to some fraternal twins. Fraternal twins usually result when two eggs are released from the ovaries, and each egg is fertilized by a different sperm cells. This results in two separate and genetically distinct embryos. Since specific genes can cause a woman to hyper-ovulate, and release more than a single egg during each menstrual cycle, the tendency to have fraternal twins can be passed along in families carrying those genes. But still, most twins will not give birth to twins.

   Nutrition may also increase the odds of having fraternal twins. The highest rates of fraternal twinning in the world are found in certain parts of West Africa where a lot of cassava is eaten. The peel of this potato-like root is thought to contain a substance that causes women to hyper-ovulate.

-Sean Kenniff, MD