Different Types Of Twins

Learn about the different types of twins and what your chances are of conceiving them.

Everyone everywhere seems fascinated with twins. It doesn't seem to matter whether they are boys or girls or both. But one thing frequently inquired about is if they are identical or fraternal and even some people don't know the difference in the two types of twins possible.

Identical and fraternal twins are the two types that occur. Simply put, identical twins are identical in their genetics and fraternal twins are no more alike that any brother and sister. Identical twins must always be the same gender while fraternal twins can be boys, girls or both.

Identical twins are also called monozygotic and they result from the fertilization of one egg by one sperm which splits after fertilization and results in two babies being formed. Each twin develops from the identical half of one fertilized egg.

Identical twins always have the same features since they have the same genetic makeup. Their hair, eye color, blood type, body scent and dental impressions will be exactly the same.

Some identical twins are also called mirror twins because some of their features are related in a mirror-like manner. For example, if one twin is right-handed the other will be left-handed.

Fraternal twins are also referred to as dizygotic which results when two eggs are fertilized by two sperm. These twins may or may not look alike and really only are two siblings who share the same uterine growing space.



Half the fraternal twins in the world are same-sex and the other half are male-female. One factor relating to the incidence of fraternal twins is age. The older a mother is when she conceives the more likely she is to have fraternal twins. This is especially prevalent after the age of 35.

Some fraternal twins can even be conceived on different days in the reproductive cycle. On rare occasions superfetation may occur when a second egg is fertilized in a following cycle, resulting in two babies due at different times. It rarely happens because of the circulating hormones which are initiated with the beginning of pregnancy.

Twinning rates will also vary with the race of the parents. Less twins are born to Asians than any other race yet the Japanese are more likely to have identical twins rather than fraternal twins.

Twins are more likely to occur in larger families as well. This also goes along with the increased twinning rate in older mothers for those are the ones more likely to have more children.

New fertility treatments are greatly increasing the twin rate beyond what it was in previous years. Today, at least 20 percent of pregnancies conceived with one medication called Pergonal, will end up having twins.

Fraternal twins are also the hereditary kind. It is one of the most frequently asked questions of twin parents. Some don't know the family history while others do. When someone asks if twins run in your family and you had identical twins, you can tell them it doesn't matter because it is fraternal twins that are hereditary.

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