December 6, 2011

where twins come from


Chikezie [right] and his fraternal twin brother Chigozie [left]. 

Most people don't really understand the genetic predetermining factors that can lead to having twins. I didn't either until I was pregnant with them and wanted to know how/why/what etc. I often find myself just nodding and going along with people telling me all about why they think they'll have twins or because Chikeize is a twin, no wonder we had twins. Others think that because my mom had triplets, that is why we had twins. However, those two factors were merely coincidences in our twin pregnancy. And I'm about to explain why.

There are two different categories of twins, identical and fraternal

Identical twins are formed when one egg, fertilized by one sperm, splits into two, thus, two babies. Identical twins are completely random. Everyone woman has an equal chance of having identical twins. It has nothing to do with the male's genetics or the female's; it just happens by chance. (There are a lot of cases that prove the exception to this rule and there is still research being done on this. But for now, this is how they think it works.)

My friend Megan's identical twin girls, Ainslee and Kylee. 

So, if your sister in law had identical twins, your chance of having identical twins, or any twins at all is not increased. 

Fraternal twins are made when a woman hyper-ovulates and releases two eggs and both eggs are fertilized by two separate sperm. Fraternal twins are determined by the female's genetics. It is the male's genetics that determine the gender of the baby...so if you want to guess the genders of future children, looking to your partner's family history may give you some clues.

There are some influencing factors that can increase the odds of having fraternal twins:
  • Family history: If the female has history of twins in her family. 
  • Increased weight and/or height.
  • Increased age (women 30-45 have been shown to have a higher frequency of twin pregnancies)
  • Having had a previous multiple pregnancy. If you already had a set of twins, you are more likely to have another set.


That being said, in our case, the fact that Chikezie is a fraternal twin had no genetic bearing on our twin pregnancy. Also, my mom had triplets through IVF, which also had no link to our twin pregnancy. There are a couple of twins in my lineage which could have been an influencing factor. I've also read that it's quite common for women to hyper-ovulate, so maybe that's what happened!

There you go, people. A little lesson in where twins come from. 

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