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Thursday Thirteen – Thirteen FACTS about Twins

March 15, 2007

I was over at Yahoo! Answers because someone forwarded me a question from there about twins. I was shocked at all the misinformation that is out there. So here are 13 facts about twins:

1. Monozygotic or “identical” twins are from one fertilized egg that splits. It’s completely random and ALL pregnancies have a 1 in 250 chance of being identical twins. They are not influenced by maternal age, family history, fertility drugs, etc.

2. Dizygotic or Fraternal twins occur when the female produces more than one egg and both are fertilized.

3. Factors that impact your chance of having fraternal twins include age (older you are the more likely), ethnicity (more common in African Americans, less common in Asians and Hispanics), the use of fertility drugs, and family history. Over at they have a ton of other factors that I don’t have room to list.

4. Twins have become more common because of the use of fertility drugs and procedures such as IVF. This does not mean that you it’s okay to ask someone on the street if they used fertility treatments to have their twins. Would I ask you how many time you had sex to conceive your children?

5. It’s ten times worse if you ask “Are they natural?” when you really want to know if someone used fertility treatments.

6. Fraternal twins can run in families. They also walk and crawl.
(All kidding aside, there is research that suggests there is a gene for “twinness” that is an inherited trait.) There is an increased chance of having fraternal if there is a family history of fraternal twins in the female’s side. So if the female’s mother or father has twins in their family that are fraternal and were not due to fertility drugs then this counts as family history of twins. The male’s family history doesn’t count because no matter what crazy things you might do in bed, there is nothing the father can do to make the mother produce two eggs.

7. However, a male with a family history of twins can pass down the “twin gene” to his daughters and will have an increased chance of having fraternal twin grandchildren. This may be why there is the myth that twins skip generations. Either that or people don’t understand “increased chance” doesn’t mean guaranteed.

8. So, in case you didn’t understand what I meant by 6 and 7: If you are female please don’t write how your husband is a twin, and his sister has twins and his mom is a twin then ask what are your chances of having twins. HIS history doesn’t count.

9. Identical twins have identical DNA. This does not mean they will look exactly alike. In fact, identical twins have different fingerprints.

10. Identical twins are not identical. Mine are identical and have very different personalities, different cries and facial expressions. They are not interchangeable and should be looked upon as individuals.

11. Identical twins cannot be boy/girl twins. If don’t know how boys and girls are different then you are either too young to be online by yourself so ask your mommy/daddy or you need to take Anatomy over again. (I can’t tell you how many times I’ve been stopped with: Are they twins? Me: Yes, they’re identical twins. Stranger: One boy, one girl?)

12. Fraternal twins are as similar DNA wise as any other siblings. They don’t ask you why you and your younger sister don’t look alike. It’s not necessary to tell them they don’t look alike. They can be boy/boy, girl/girl, or boy/girl.

13. I don’t know why this one fascinates so much but it seems to be asked alot so here goes. If a female set of identical twins marries a male set of identical twins biologically (DNA-wise) the resulting offspring from both sets would be siblings. Emotionally and legally they would be first cousins.

Thanks for letting me rant a little. If you’re a twin parent and have a funny story about twin misinformation link it in the comments and I’ll add a link in this post.

3 Comments leave one →
  1. carrie permalink
    March 15, 2007 10:54 pm

    nice blog! i will have to send some business to this post to clear up some twin ignorance!

    my husband is an identical, mirror-image twin. so naturally everyone when i was pregnant was convinced i was going to have twins. ugh…i got so sick of answering the “are you afraid of having twins?” question.

    i of course ended up with the “good” twin. i tease his brother that he is the “evil” twin!

  2. Anonymous permalink
    March 16, 2007 9:43 pm

    Mommy Brain,

    I thought you struck a chord when you posted a comment on my blog (trials of trace in adoption la la land) before, and this might sound totally weird, but are you an online DelcoFlyBaby?


  3. Swistle permalink
    March 20, 2007 6:57 pm

    This is really good. I have boy-girl twins, and people are always asking me if they’re identical or fraternal. Actually, some people ask me if they’re identical or “paternal.” Whuh?

    I read recently that they think identical twins MIGHT run in families, at least SOMETIMES. They started researching this because of the families that have way more than their statistical share of identical twins. They’re wondering if there’s a genetic tendency for a zygote to split, just as there’s a genetic tendency for a mother to produce more than one egg at a time.

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