Posted by: urbanadventurertales | September 16, 2009

Twin Tuesday!

In keeping with my weekly “Twin Tuesday” post, I thought I’d post a little educational piece about twins.

I have often heard people ask, “Are they maternal or paternal?”  What they really mean to say is, “Are they identical or fraternal?”

*Side note:  If you look at this picture of my twins, you can clearly see that they are NOT identical 🙂

So, statistically the most common twins are fraternal.  Fraternal twins are conceived when the mother releases two eggs and both are fertilized by different sperm.  Essentially, fraternal twins are no more genetically connected than biological siblings.  The chance of a woman conceiving twins naturally (without the help of fertility treatments) is 1 in 60.  This rate increases if twins run in the mother’s side of the family.  My aunt has twins, therefore the tendency does run in my family.  The probability also increases with age.  Women over the age of 45 are 10 times more likely to conceive twins than women in their early 20’s.  This is due to the fact that they often release more than one egg during a cycle as they get older.

Identical twins are conceived when one egg is fertilized by one sperm and then splits into two embryos.  Rarely, an egg can split prior to fertilization and can be fertilized by two sperm, causing partial-identical twins.  Identical twins ARE NOT hereditary (meaning they are not passed down from generation to generation).  It is simply a fluke.  But is a common misconception and often asked.  The chance of having identical twins is 1 in 250.

The average single baby is born at 39-40 weeks gestation.  The average twin birth occurs at 36 weeks gestation.  Mine were born at 37 weeks.  The average single baby is 7.5 lbs.  The average twin is 5.5 lbs.  Mine were 6.0 and 5.3 lbs. each.

About 50% of twins are born vaginally.  40% are both vertex at the time of birth.  40% are vertex/breech (this is the case of mine and they were delivered via c-section).  8% are both breech.

More fun twin facts to come next week!  Stay tuned 🙂



  1. I get asked this same question about my boy/girl twins…Uhhh…Yeah… So I’m glad it’s not just me.

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