Are Twins Genetic? What Are the Chances of Having Twins?

Are twins genetic? And what else could influence your chances of having twins? We take a look at the science behind multiple births. Is conceiving twins genetic? Or do other factors influence your chances of having twins? We’ll look at how twins are conceived and what role genetics plays. Let’s dive in.
In this article: 📝

• Are twins genetic or hereditary?
• Which parent carries the gene for twins?
• Can you have twins even if they don’t run in the family?
• What are the chances of having twins if it runs in the family?
• Are twins genetic? The bottom line

Are twins genetic or hereditary?

There are two main kinds of twins: fraternal and identical. Fraternal (or dizygotic) twins are less likely to look the same because they come from two different eggs and are fertilized by two different sperm cells. Identical (or monozygotic) twins, on the other hand, come from the same egg. So, is conceiving twins genetic? Well, it depends on the kind of twins we’re talking about.

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Are fraternal twins genetic?

We know that fraternal twins run in families. And recently, scientists have identified two specific genes that tell us more about why. First, there is a gene known as FSHB that makes it more likely for women to release two eggs at the same time. This is known as “hyperovulation” and seriously ups the chances of conceiving twins. The other gene in question is called SMAD3. And it may have a bearing on how ovaries respond to the follicle-stimulating hormone (FSH)—that’s the one responsible for stimulating the growth of eggs in your ovaries. The research is still young on this, but this gene combo certainly makes a good argument for why fraternal twins pop up in multiple generations of a particular family.

So are identical twins genetic too?

Until recently, scientists had no idea what caused an egg to split in two. It seemed to be random. But new research suggests it’s the result of something called DNA methylation. This process changes how genes are expressed, but it’s not itself genetic (as in it’s not passed down your family line.) If all that sounds complex—it is! And scientists don’t yet fully understand how it works. But the takeaway is that while fraternal twins run in families, identical twins don’t seem to.

Which parent carries the gene for twins?

Both parents can carry the gene that affects ovulation. But it will only have a practical effect for the partner who ovulates. In other words, if twins run on the dad’s side of the family, it won’t affect his chances of having twins. But if he has the gene, he could pass it onto his daughter, meaning she would have a higher chance of twins. That’s the reason people sometimes talk about twins “skipping generations.”

Can you have twins even if they don’t run in the family?

The chance of fraternal twins is higher in families where there’s a genetic predisposition. But that doesn’t mean that people without that family history can’t have twins. A range of other factors also affects the chances.

The mother’s age

Mamas-to-be over the age of 35 are more likely to have twins. Their bodies are releasing more of the hormone that stimulates ovulation. That increases the chances of two eggs being released and fertilized at the same time.

Mama’s diet and build

Vegan women seem to be less likely to have twins than those who consume milk. And women with a BMI higher than 30 are more likely to have twins.

Pregnancy history

Twins are more common in second or later pregnancies and with women who’ve already had twins or multiples. They’re nine times more common for mamas who got pregnant while still breastfeeding.

Fertility treatments

Some fertility treatments or drugs increase the chances of multiple births.

What are the chances of having twins if it runs in the family?

So, if there are twins in your family, what are the chances you’ll have them too? If the twins are on a male partner’s side of the family, they won’t affect the odds at all. The same goes for identical twins anywhere in your family. But if there are fraternal twins on your side of the family, you may carry the gene that increases the chances of hyperovulation. Women who are themselves fraternal twins have one pair of twins for about every 60 live births. For men who are fraternal twins, that rate is 1 in 125. But as we’ve seen, lots of factors besides your family history influence your chances of having twins.

Are twins genetic? The bottom line

Conceiving non-identical twins has a link to your genes, but it’s not the whole story. And your genes don’t seem to influence your chances of having identical twins at all. If you’re already the mama of twins—or you have a set on the way—we have a Peanut group especially for you. See you there!