Twins & Multiples

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Fraternal Twins With Different Fathers: Is It Possible?

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Families with siblings that have different fathers are pretty common. But how about fraternal twins with different fathers? Is this a possible phenomenon or simply a question that can never be answered?

As impossible as it may sound, it is actually possible; however, very rare. The hows can also be pretty perplexing but once you know about a woman’s cycle, it is plausible to have two men impregnate a woman at the same time.

This is what happened to one woman in Vietnam.

So, how do fraternal twins with different fathers happen?

A set of toddler twins in Vietnam broke the internet and the science community in 2016 when they turned out to have different fathers.

From their physical appearance, it was quite clear that the two didn’t look alike. According to the Washington Post, one of the babies had thin, straight hair while the other has thick, wavy hair.

After their family members have been very vocal about the twins’ great difference in appearance, a Vietnamese couple brought their twins to a specialist.

Their DNA was tested at the Center for Genetic Analysis and Technology. They found out that the twins were a pair of bi-paternal twins – fathered by two completely different men.

This was pretty rare not only in their country but also in the world.

Another case of twins fathered by different fathers were Marcus and Lucas, twins of mom Charlotte Hilbrandt. After having sex with both his ex-husband and new lover, Charlotte got pregnant and later on gave birth to the boys.

Couple holding mother's womb

How can this happen?

So, can twins have separate fathers? Studies have actually shown that it is indeed possible for a woman to get pregnant with two different fathers at the same time. This phenomenon is known as superfecundation.

Simply put, superfecundation is when two eggs from the same woman is fertilized by two different men during the same ovulation period.

A normal ovulation cycle actually just lasts 24 hours. If it doesn’t get fertilized by a sperm, the egg and the uterine lining will shed – which then leads to menstruation.

To make it a lot easier to comprehend imagine this: if a woman has sex with two men within 24-hours, these men have a great chance of getting her pregnant at the same time with twins.

Still, this is a one in a billion chance. There are only very few reported cases of superfecundation twins.

How rare is heteroparental superfecundation?

Heteroparental superfecundation is actually quite common among animals. It has been reported in cows, dogs, cats, and rodents.

But what about for us humans?

The chance for one sperm to fertilize an egg is small in normal conception. This is because the journey that a sperm takes to reach the egg is arduous – with a long journey through a harsh reproductive system where white blood cells see sperm cells as invaders.

Therefore, the chances of two sperms, especially from two different men, are rather rare.

However, according to a study, they estimated that two different men can father a pair of twins in one out of 400 or 0.25% of twin births in the USA. There has also been another study that reported that there is a frequency of 2.4% among non-identical twins whose parents were involved in a paternal suit.

The only reason why there is only an estimate is that superfecundation cases only happens or arises whenever a family member is suspicious of a twins’ paternity. There might be other cases still left undiscovered due to lack of DNA testing.

Fraternal Twins With Different Fathers


Apart from superfecundation, another rare phenomenon surrounding twins with different fathers is known as superfetation. This is when a woman gets pregnant while she was impregnated. This happens when another, completely different ovum gets fertilized during an ongoing pregnancy.

Usually, this takes place weeks after the first egg is fertilized. Fertilization can happen from a sperm of the same father or a different person.

For this to successfully happen, these scenarios must happen:

  1. The release of an ovum during pregnancy – This is nearly impossible since ovulation ceases once a woman is pregnant.
  2. The second ovum is fertilized by a sperm cell – If another egg is indeed ovulated, a sperm should be able to fertilize it. Then again, this is more or less unlikely to happen as the pregnant body creates a mucus that stops sperms from entering.

Most known cases of superfetation in humans happens when the women got fertility treatments.

During in vitro fertilization, fertilized embryos are transferred to your uterus. Superfetation can happen if you ovulate and the egg is fertilized after the embryo has been transferred to your womb. Heteroparental superfetation can happen if the sperms that fertilized the eggs were from different men.

Suffice to say, the embryos that are now in your womb are twins seeing as they shared the same body during a pregnancy. However, one of them is more developed than the other and this can cause some complications during their birth.

Are all twins that do not look alike bi-paternal?

Just because a pair off fraternal twins do not look alike doesn’t mean they are bi-paternal. There are actually many cases of twins that look nothing alike – with some even looking like they are from different races.

This is because fraternal twins are basically siblings who shared the same womb. Unlike identical twins where an egg split into two, fraternal twins came from two different eggs. With even the same parents, they only get 50% same DNA.

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It is amazing to see news about fraternal twins with different fathers, simply because it is something that shouldn’t have happened.

The body can do wonders and even in an advanced age as today it is still hard to comprehend how some things around or within us work. But thanks to these cases, we can slowly unravel the mysteries of the human body.

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