What Are Your Chances of Having Twins?

Ah, twins. An idea that evokes both fear and delight.

When the subject of twins arises, someone typically chimes in, “Twins run in my family!” But is that really possible? There are plenty of misconceptions (no pun intended) when it comes to twins, including the following:

Identical twins run in families

This is simply not true.

Identical twins are spontaneous. They occur when a fertilized egg randomly splits into two identically-genetic zygotes. It is for that simple reason – spontaneity – that identical twins cannot be “passed down” through the generations. Multiple sets of identical twins in a family is pure coincidence.

The other possibility is fraternal twins appearing identical. Mary Kate and Ashley Olsen are famous for playing one child in Full House in the early 90s, leading everyone to believe they were identical twins. But the two are fraternal, meaning they look so much alike just as any other siblings would look alike.

Why is this relevant? Because fraternal twins, on the other hand, can run in families. Fraternal twins occur when multiple eggs are released by the mother in the same cycle, are fertilized, and implant. The body’s likelihood of releasing multiple eggs in one cycle can be passed down.

Fathers contribute to a couple’s likelihood of twins

Nope. While fathers can carry the gene that contributes to fraternal twins, it can only affect the couple if it’s the mother who has it. Why is this? Well, it’s because the mother is the one doing the egg-dropping. Even if the father carries the gene, he can’t give it to his wife during conception, so it has no relevance.

Where that gene is relevant (stay with me) is if that couple were to conceive a daughter. He could then pass down that gene to his daughter, which would affect her likelihood of having fraternal twins.


All twins have more genetic links than typical siblings

This is only true of identical twins. Because identical twins are two babies split from the same egg, their genetic make-up is exactly the same. Since fraternal twins are from two separate eggs, they are no more the same than any other set of siblings.

After one set of fraternal twins, the likelihood of another set quadruples

This is because women who release more than one egg naturally have a higher likelihood of doing so again. So, if a woman has already had one set of fraternal twins, she is four times as likely as another woman to have another set.

The number comes out to about 1 in 3,000 of having another set.

Other twin statistics

What are some other factors that play into a woman’s likelihood of having fraternal twins?

  • Age: Women over the age of 35 are more likely to release multiple eggs in the same cycle than other women. This is due to hormone fluctuations.
  • Nationality: African-American women are more likely to conceive twins than Caucasian women.
  • Number of Children: If you’ve already had a few children, the chance that you’ll have twins goes up. Perhaps it’s because you’re playing the odds or simply a correlation that you must be good at getting pregnant if you’ve already had children.
  • Fertility Treatment: Women undergoing fertility treatments are more likely to conceive multiples because the drugs they are taking stimulate egg production. This increases the chance of more than one egg being released at a time.

Whether you’re all for twins or are terrified at the idea, you at least know your chances when you roll the dice!

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