So, now that the twins are here and I've been a little more mobile, I've noticed quite a few stares and have gotten some pretty interesting questions. I still don't understand why people ask me if they're boys when they're wrapped in pink blankets but whatever! I've decided to post some information about twins. Actually, when Paul and I found out we were having twins we did a lot of research and read a lot of books so that we were well informed.
There are two different types of twins; fraternal and identical. Fraternal is when two eggs are fertilized. These babies are no more related than any other set of siblings. They can be boy/boy, girl/girl or boy/girl. When they are the same gender, doctors may suggest an amniocentesis to see if they are identical or fraternal. Depending on when the egg splits in identical twins, they may not share the placenta, sac, or chorion. Sometimes fraternal twins share a placenta, but only when it fuses together. They do not share an amniotic sac or chorion. Fraternal twins can look very similar or nothing alike. The result of fraternal twins has nothing to do with the man's genes. The woman's genes, in the case of spontaneous twins determines whether or not twins happen. Her father's genes and her mother's genes influence her ability to produce fraternal twins or higher order multiples.
Now for identical twins. There are three types of identical twins. There's diamniotic/diachorionic, diamniotic/monochorionic, or monochorionic/monoamniotic twins. Identical twins are always the same gender. They are a result of one egg splitting randomly. Genetics has nothing to do with identical twins. They are genetically the same, technically clones of each other.
As for our twins, they are diamniotic/monochorionic identical twins. They split on day six. They shared a placenta and chorion (outer membrane) but had different amniotic sacs. We've also learned that our twins are pretty rare (we knew they were special!). We learned about our twins at an ultrasound appointment at about week 20. It didn't take the doctors long to figure out what type of twins they were because of the things they shared, but they do test the placenta after birth to "be sure".
Anyway, I just thought I'd share what we've learned about twins.