Fraternal Twins: 7 Fascinating Facts About Double Siblings

Brush up on some surprising truths about fraternal twins.

How twins come into this world is nothing short of miraculous, and fraternals have their own unique presentation that in some cases diverges radically from identicals. Sometimes it’s even hard to spot fraternal twins because they don’t always look alike at all.

Because identicals tend to get all the glory, we thought it would be fun to take a look at the facts surrounding fraternal twins, which is no less compelling, and if you are a parent to fraternal twins, you might even learn something new.

  1. Fraternal twins form from two separate eggs. Unlike identicals, which form from one egg, fraternal twins form from two separate eggs, which is also known as dizygotic. Monozygotic twins form from a single egg and sperm that splits into two after conception. So fraternals are more like two separate conceptions that develop side-by-side.1
  1. A fraternal twin set can be either one gender, or a combination of a boy and a girl. Because of the nature of the conception, fraternal twins can look very different, and can be a combination of genders. The father’s sperm determines gender, as I’m sure we all remember from high school biology: XX for a girl, and XY for a boy. So dizygotic twins can just as easily be boys, girls, or a combo1.
  2. Fraternal twins vary widely in appearance and personality, like regular sibs. Monozygotics (identicals) who share the same DNA (because they come from a single egg that splits) often have that doppelganger thing happening: they aren’t exactly alike but they usually look very similar. Fraternal twins tend to be more like other siblings and when some of them share physical similarities, it’s a crapshoot, genetically speaking, as far as likenesses in appearance and personality.
  1. Fraternal twins have two placentas. As we have learned, fraternals are like two separate babies developing side by side, so they each get their own amniotic sack and placenta. So if you are in your first trimester with fraternal twins, your body is working extra hard! However, something can happen during development where in a multiple pregnancy the two placentas can fuse together, making it difficult to determine zygosity in utero1.
  1. Fraternal twins can be conceived at different times or by different fathers! It’s really unlikely, because one egg is released during ovulation at a time. But some women experience something called hyperovulation, where multiple eggs are released. While the first egg is on the course of implantation, another egg is released and fertilized. This phenomenon is known as superfetation. So it is technically possible, though very rare, that fraternal twins could have different fathers2.
  1. Fraternal twinning presents differently across racial and ethnic lines. Not all races and cultures have the same rates of twinning, and twins have skyrocketed in the West due to fertilization techniques. Some ethnic groups have twins much more frequently, for example in Central Africa populations, whereas Asia and Latin America had the lowest rates of twins2.
  1. Fraternal twins can be the result of fertility treatments. Many of the twin births in the U.S., 36% to be precise, are the result of fertility intervention3. Because doctors are using multiple eggs in the procedure, it’s possible for IVF (In Vitro Fertility) twins to be fraternal, however, the treatment often sees identicals occur for mysterious reasons4.


The more we learn about twins, the more we want to learn, and as parents nothing could be more exciting than watching this special phenomenon unfold in our own lives. It is safe than it ever has been to give birth to multiples, but if you have had the first ultrasound, and you are expecting two bundles of joy, stay up on the facts and check in with your care workers so that you are taking the best care of yourself possible. Fraternal twins have all the advantages of twins, and no less capacity to enjoy the deep bond and connection that identical twins have.  





About Susie Almaneih

Susie Almaneih spent several years during her young adulthood teaching children dance at her church group, as well as other cultural-based activities. Susie now spends as much time as she can giving back to the families in her community. Over the years, this love for community has evolved into a deeper love for delivering positive and creative content and awareness to families of all ages.

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