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My husband and I have fraternal twins. Now his brother is having fraternal twins. What are the odds of this happening? All the research I have read says twins are a maternally controlled trait. Is it just luck?
–Emmy
It’s just luck! Fraternal twins do run in families, but only on the egg-production side. There are genetic variants that make people more likely to release multiple eggs at once, which increases the chance of twins. But egg release is the important factor (there is always a lot of sperm).
The rate of fraternal twin birth is around 2.3%. So the chance that any two couples have twin births is about 0.05%, or about 1 in 2,000. Meaning it’s unlikely but not near impossible —better than your odds of winning the lottery, for example.
Fun fact: people talk about twins “skipping a generation.” The reason you will sometimes see this is that a father can pass the genetic variant that affects twins to his daughter, even if it doesn’t affect his own chance of having twins. So grandma having had twins may express itself in a granddaughter also having them.
Enjoy your many lucky babies!
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We have a good friend who had fraternal twins boy and girl and then had identical twin boys. What are the chances of that?? Haha
My grandpa was a fraternal twin and his two older brothers were too. Poor great grandma! But fortunately(?) that trait doesn’t seem to have been passed down to my mom or me.