Do Fraternal Twins Run in Families?

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Identical twins are less common than fraternal twins.

Fraternal twins are the most common of all twin babies and occur up to 75 percent of the time. Fraternal twins have two placentas that can fuse into one, but unlike identical twins, fraternal twins are no more genetically similar than any two siblings with the same biological parents. Like identical twins, fraternal twins can look very much alike, making it difficult to distinguish whether they are identical or fraternal.

  1. Occurrences of Twins

    • Twins account for around 90 percent of multiple births. Identical twins occur when a fertilized egg splits into two separate embryos to make two babies. Fraternal twins occur when two eggs are fertilized by two separate sperm. This leads to the formation of two embryos and makes two babies. The instance of multiple births and twins occurs most commonly in African women and more often in women who are tall and large than in women who are small and petite.

    Conception of Fraternal Twins

    • You are more likely to conceive fraternal twins through the use of fertility drugs. If a woman has already given birth to a set of fraternal twins, she is twice as likely to have another set if she falls pregnant in the future. The more pregnancies a woman has had also increases the likelihood of the woman conceiving fraternal twins. Also, the older a woman is the greater the chance of her having fraternal twins; this is due to hormonal changes in older women.

    Fraternal Twins in Families

    • Identical twins happen by chance, whereas fraternal twins are hereditary and run in families. The tendency to conceive fraternal twins is carried by the woman -- if you are a fraternal twin or are related to fraternal twins, you are three times more likely to have a set than someone who has no instances of fraternal twin births in her family.

    Identification of Fraternal Twins

    • It can be difficult to determine whether twins are fraternal or identical at birth because sometimes identical twins are born with their own individual sets of membranes, making the parents assume that they are fraternal. One way to find out is to have both babies DNA-tested. Identical twins share the same genetic information, while fraternal twins only share around half. A DNA test can be done by taking a sample of cells from the inner cheek or by having blood group examinations.

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