Are they identical or fraternal????

So yesterday afternoon we saw a perinatologist (that's medical speak for someone who specializes in high risk pregnancies). We got another sonogram and the doctor discovered that we are having identical twins!!! This only occurs in about 4 out of 1000 births, so it's pretty rare. We still don't know the sex but we should be able to tell in about 5 or 6 more weeks. So the big questions is: How do you know they are identical? Here's a little twin biology 101.

1. Identical twins occur when one fertilized egg splits into two sometime shortly after fertilization. (Fraternal twins occur when two separate eggs are fertilized).
2. Nobody knows why the split occurs, and identical twins are not genetic/hereditary like fraternal twins are. They are just a fluke of nature!
3. Depending on how soon after fertilization occurs, the twins can either develop their own placentas and amniotic sac, or share them.
* If the split occurs within the first 2 days of fertilization then the twins will each have their own amniotic sac and own placenta- this only occurs in roughly 30% of twin births and is hard to distinguish from fraternal twins since fraternals always have their own sacs and placentas.
* If the split occurs within 3-8 days after fertilization then the twins will share one placenta but develop their own amniotic sacs- this occurs in roughly 70% of twin births. This is the case with our twins- the doctor saw one placenta but two sacs!!
* If the split occurs 9-12 days after fertilization then the twins will share one placenta and one sac- this is very rare (only 1% of twin births) and very "high risk" because of the risk of entanglement with each other's umbilical cords while in the same sac. We are very thankful this is not the case with us!!
*If the split occurs after 12 days then you get conjoined or siamese twins...again, very thankful this is not the case with us!!
4. Identical twins are ALWAYS the same sex since they come from the same DNA, but interestingly, they don't have the same fingerprints!!!

So there's a little lesson on twins. I think I've covered all the questions about twins that have been asked to me over the last 24 hours...but ask away if there is something you want to know that I didn't touch on.

Now for an update on mom and babies:

I'm great except for some bouts of vomiting lately. The perinatologist will be seeing me every two weeks to do a sonogram to monitor the babies and the condition of my cervix to make sure I don't go into premature labor. I will also being seeing a cardiologist monthly to monitor my heart and make sure everything is good there. My regular OB will see me monthly until delivery gets closer and then every two weeks. I'm in very capable and intelligent hands with all my doctors and will be seeing someone at least weekly, so I feel very comfortable about everything.

The babies looked great on the sonogram yesterday. Both are developing normally and have very strong heartbeats. We did a nuchal fold test (a Down Syndrome screener) and both passed with flying colors...no concerns from the doctor. Baby A was very active- lots of tumbling and acrobatics. He would not be still and the sonographer had a hard time getting some good pics. His heart rate was 180 from all the activity! Baby B on the other hand was very calm and appeared to be napping. He stayed in one spot and posed very well for his pics- his heart rate was a little more calm at 167. Anywhere between 160-180 is a good heart rate at this stage of the game.

Yes, I am referring to them has "he" because I have to call them something, and because my gut feeling is that they are boys....I will be sure to let everyone know when we get a confirmation!