Friday, February 17, 2012

All About Twins

I have learned a lot about twins since finding out we have a set on the way.  Some of it is so fascinating, I thought the rest of you might want to know:

- Some twins share both an amniotic sac and a placenta.  These twins are always identical and this is a very rare and extremely high-risk pregnancy.

- Some twins share a placenta but have separate amniotic sacs; these are also always identical and this type of pregnancy also carries a higher risk.

- Some twins have separate amniotic sacs and separate placentas.  This type of twin is often fraternal but sometimes identical.  (YES -- it's possible to have identical twins with separate sacs and placentas!)  If these twins are born the same gender, there is no way to tell if they are identical without a blood test. 

Note:  I am pregnant with this third kind of twin.  And no, we are not going to find out the gender(s) in advance!

- Identical twins do not run in families.  They are completely random, a "fluke" of nature, and have nothing to do with genetics.

- Fraternal twins do run in families -- but only in the mother's line.  So there's no sense asking a mom of twins whether twins run in her husband's family!

- If you see a set of girl/boy twins, they are fraternal!  There is no possible way identical twins can be different genders.

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