Turns Out Fraternal Twins Really Do Run in the Family

Having twins? You might have your genes to thank for it.

Four-week-old fraternal twin boys in a moses basket Katrina Elena/Shutterstock
Looks like twins do run in families—according to new research, posessing a certain pair of genes can increase your odds of birthing fraternal twins


Fraternal twins are created when two seperate eggs get fertilized by separate sperm. There's one particular gene variant, called FSHB, that increases one's odds of having twins by 18 percent. Here's how it works: This gene is linked to higher levels of the follicle-stimulating hormone (FSH), which makes it more likely that a woman's ovaries will release multiple eggs at the same time. When you have multiple eggs, there's a greater chance that more than one will be fertilized.


Another genetic variant comes into play as well. It's called SMAD and it increases your chances of having fraternal twins by 9 percent.  Women who have both genetic variants have a 29 percent increased chance of having twins.


More: Little-Known Facts About Twin Pregnancies


"There's an enormous interest in twins, and in why some women have twins while others don't," study author Dorret Boomsma, Ph.D., said in a release for the study. "The question is very simple, and our research shows for the first time that we can identify genetic variants that contribute to this likelihood."


Researchers performed genetic analysis on over 5,500 women who had conceived fraternal twins, both with and without the aid of fertility treatments. They also studied the genetic information of more than 300,000 women who did not have twins.


The research is still ongoing and could represent a breakthrough in infertility research. According to the study's authors, FSH is injected to stimulate the ovaries and eggs for IVF but some women's ovaries respond too strongly to this. The researchers plan to create a genetic test to identify women who are at risk for this issue. 


More: New Discovery to Improve IVF Success Rates


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