The big announcement & a science lesson

Okay here is the big announcement.

Baby A is a girl.

And Baby B is also a girl.

I thought from the very beginning that I was pregnant with a girl and then when I found out I was having twins I kept thinking they were both girls. Brandon was the same way. We are very excited to know that we were right. (Especially since we have been wrong about so many other things during this pregnancy)

I know that you are now all wondering whether the girls are fraternal or identical. I'll tell you, but first I'm going to give you all a quick science lesson about the difference. A lot of this stuff I didn't know until a few weeks ago, and I think it is pretty cool. So while I have your undivided attention I will educate you as well.

FRATERNAL TWINS (dizygotic)

Fraternal Twins are the more common type of twin. Roughly 2/3 of all twins are fraternal. Here is how they develop.

A woman's body is supposed to release 1 egg a month, but it can produce more than 1. If that happens and each egg is fertilized by the father's sperm then two babies will develop.

Fraternal twins can be 2 girls, 2 boys, or one of each. I like how one book I read puts it, “they are essentially siblings born at the same time.” Brandon and his twin brother Bryan are fraternal twins.
You may have heard that twins come from the mother's side and skip generations. That can be the case with fraternal twins. The mother may have a genetic disposition that allows her to release more than one egg at a time. The father's genes have nothing to do with it. So even though Brandon is a twin he has no influence on whether or not I release extra eggs.

One other thing about fraternal twins; since they develop from separate eggs and sperm they develop separate placentas. This will be important in a second.

IDENTICAL TWINS (monochorionic)

The other 1/3 of all twins are identical twins. Here is how they develop:
1 egg is fertilized by 1 sperm- just like with a normal single birth baby. After fertilization the now fertilized egg (called a zygote) splits into two zygotes. Each of these will develop into a baby.

I used to think that the split happened in the moments right after fertilization, but it actually can happen anytime during the first 8 days. Pay attention to this because this is important too.

If the split happens:
• Within 3 days of conception the twins will have 2 separate placentas. (They will also have two chorions (the outer layer of the sac that contains the fetus) and two amnions (the inner membrane of the sac containing amniotic fluid))
• Between 4-7 days the twins will have a shared placenta. (They will also share the chorion, but have separate amnions)
• After the 8th day the twins will share a placenta. (They will also share the chorion and amnion)

About 68% of all identical twins are they type where the split happens between days 4 and 7. By the way, no one really knows what causes the zygote to split. It has not been linked to heredity, nor can any other theory successfully explain what triggers the split. It just happens.

WHAT WE ARE HAVING:

Now I'll tell you what our girls are. The answer is . . . they appear to be sharing a placenta. If you've been paying attention then you know that means they are probablty identical! (I should add that it is possible they are fraternal and their placentas developed close together. However, there is only a slim chance of that.)

I think the only people who guessed right were my friends Alicia and Heather, my cousin Melissa, my brother in law David, my sister in law Shannon, and my sister Lindsey (I accidentally slipped and told her I am planning on painting the babies toenails to tell them apart when they are first born).

Thanks for playing along with my family's little guessing game. Later when we get closer to the due date we will have the second round of guessing for what day the babies will be born, what they will weigh and how long they will be.

Most of this info was gathered from The Everthing Twins, Triplets, and More book by Pamela Ferrro. And When You're Expecting Twins, Triplets, or Quads by Dr Barbara Luke and Tamara Eberlein. The diagrams are mine :)