Can Fraternal Twins Have Different Fathers?

This post forms part of an ongoing series that looks deeper into twins and what makes them special.  Today’s question we see asked quite a bit – Can fraternal twins have different fathers?  We look at whether fraternal twins can have different biological fathers, why this is an occurence and how rare it truly is (spoiler alert – 0.25% pregnancies can have twins with different fathers).

Other posts in this series on twins include:

Can Fraternal Twins Have Different Biological Fathers?

Short answer – Yes but rare!

Long answer –  While very rare (we’ll get to that shortly), fraternal twins can have different biological fathers thanks to something called heteropaternal superfecundation.

What is heteropaternal superfecundation you ask? This is when two or more egg cells are fertilised by different acts of sexual intercourse which can then result in twins being born to different biological fathers.

Interestingly, heteropaternal superfecundation can occur within a few hours to a few days. This is due to the sperm cells being able to live inside a female’s body for up to 72 hours (3 days). During this time, if the body releases another egg,  the sperm can fertilise this egg which causes the second pregnancy to occur.  This is also known as superfetation.

Why Do We See Fraternal Twins with Different Biological Fathers?

What’s important to note here is why this is a phenomena is linked to fraternal twins? As we mentioned earlier in the post, fraternal twins occur when multiple eggs are released and fertilised by different sperm of the same man. In the case of fraternal twins, the woman released multiple eggs however the eggs are fertilised by two different men as opposed to the eggs being fertilised by the sperm of one father. This is when you get fraternal twins with different biological fathers

If we play this out with a real world example:

Jenny has sex with one man on Sunday and then have sex with another man on Monday. When her eggs are released on Tuesday, they could be fertilised by the sperm living inside which creates fraternal twins with different biological fathers.

Under this example, the key points to note are:

  • Jenny has sex on Sunday night. This sperm can live inside her boy for up to 3 days.
  • Jenny has sex on Monday. This sperm can live inside her boy for up to 3 days.
  • Jenny releases eggs as part of her natural ovulation. At this stage, the sperm from Sunday and Monday night are both still under 3 days old and still alive.
  • It’s once Jenny’s eggs release on the Tuesday that they are fertilised by the sperm still alive.

Rarity of Twins Having Different Biological Fathers

In terms of rarity, studies have shown out of 39,000 pregnancies, they were only able to find 3 cases of twins being born with different fathers. While other studies have shown 1 in 400 pregnancies (0.25%) have witnessed heteropaternal superfecundation occuring. It really highlights how rare this can be.

It’s even thought that there might be more twins out there with different fathers than people realise however due to it being such a rare event, most people aren’t even aware that it’s something that occurs and assume they are just twins that look different. Something that’s easy to do when you have fraternal twins which can look quite different (even differing in sex).

Summary / Closing

While extremely rare (3 out of 39,000 pregnancies), it’s biologically possible that twins can exist with different biological parents. Are you reading this article and wondering whether twins you know might be of different fathers? We’d recommend looking into DNA tests which are readily accessible and won’t break the bank.

We hope you’ve enjoyed reading this article and check out other articles of ours relating to twins.

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