Alternately, the lowest rate of occurrence - six per 1,000 births - is in Asia. The rate of this type of twins in Africa is around 14 fraternal twins per 1,000 births. The highest rate of fraternal twins occurs in Africa. Besides curiosity, people usually test whether they’re fraternal twins to better understand their health conditions. This is done by swabbing each twin’s cheek. The only 100 percent accurate way to tell the difference is through a DNA zygosity genetic test. And since environmental factors can lead to identical twins having slight physical differences, many people can’t distinguish fraternal twins from identical. Here’s the thing: For all of their differences, fraternal twins could still look extremely similar - just as any siblings with shared genetic makeup can look extremely similar. They can be hard to distinguish from identical twins. When it comes to connection, identical twins have a stronger bond than fraternal ones because they share 100 percent of their DNA. This is why identical twins are usually closer than fraternal twins.

And while you’ll undoubtedly love their individualism, it can make mastering their sleep routine a bit of a nightmare. Since fraternal twins only share 50 percent of their DNA, they can have very different characteristics and preferences. This phenomenon is known as superfetation. This can take place up to 24 days after the first egg’s release, leading to twins born a few weeks apart (although they’re often born in the same general timeframe). Then the second egg gets fertilized, too. By the time she experiences another cycle, thus releasing another egg, she is already pregnant. Heck, fraternal twins may not even be born in the same week or month! How is this possible? So, let’s say a woman releases an egg during her cycle and it gets fertilized, but her cycle is interrupted. This happens when a woman releases multiple eggs (known as hyper-ovulation), has sex with more than one partner, and the eggs are fertilized by sperm from different partners. It’s a real phenomenon known as superfecundation, or bi-paternal twins. That’s right - this isn’t just something that you’ve seen in movies. Fraternal twins may have two different fathers. Of course, we are strictly speaking from a genetic standpoint - sex is determined in utero, while gender is a social construct and something a person decides for themselves later. That means fraternal twins can both be boys, both be girls, or be a boy and girl. Since fraternal twins originate from two separate sperm, each of those eggs could be a boy or girl. They can be the same sex or different.Īs is the case with any conception, chromosomes from the father’s sperm determine the gender. Remember how we said fraternal twins occur when two different sperm fertilize two separate eggs, both of which then implant in the uterus? Because they are two separate eggs when they’re fertilized and implanted, fraternal twins usually develop separate amniotic sacs, placentas, and other supporting structures. They have separate supporting structures. Around 75 percent of all twins are fraternal. People tend to talk more about identical twins (because how wild, right?), but a twin pregnancy is actually much more likely to result in fraternal twins. You know the basics, but prepare to learn some lesser-known details about this type of twin. What are some surprising facts about fraternal twins? For this reason, they’re no more genetically similar than non-twin siblings. Unlike identical or monozygotic twins, who share 100 percent of their DNA, fraternal twins only share about 50 percent. Those two fertilized eggs then implant in the uterus and grow. How are fraternal twins formed?įraternal twins develop when two separate eggs are fertilized by two separate sperm. And whether you’re expecting, trying to conceive, or just curious about twins in general, these little morsels of information are sure to intrigue.įirst, though, let’s start with a quick refresher on what exactly fraternal twins are.

But how much do you really know about this type of twins? There are some pretty darn interesting facts about fraternal twins (also known as non-identical or dizygotic) that you may not even be aware of. Have you ever met a set of fraternal twins? Many of us have - or, if not personally, we’re at least familiar with a famous set like Mary-Kate and Ashley Olsen.

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