The envelope has been mailed -- we're testing Hadley and Leila to see if they're identical or fraternal!
Here's the scientific information: when I was pregnant with the girls, they didn't share a sac or a placenta. If either of those are shared, twins are automatically known to be identical (same egg, same sperm). Since they didn't share either of them, we were told that the chances were good that they were fraternal (two eggs, two sperm). However, in a small percentage of identical twins, the egg splits early enough that they don't share anything, either.
At first, we didn't care to get the girls tested. They looked alike, but we figured that babies from the same family tend to look alike anyway, and that they would look less similar as they got older. As the months went by, it still seemed like Tony and I were the only ones who could actually tell them apart! We started to get suspicious ... but twin zygosity tests are quite expensive.
Then, two things happened: I found a company who does testing for about half of what I expected to pay. A few weeks later, I won money on a Visa debit card for playing a silly game on playdoh.com! I told Tony that I wanted to use the money on a "non-necessity" item, since we normally have a pretty tight budget. He suggested getting the girls' zygosity tested. (A zygote is an egg ... thus the term "zygosity".)
So, what do you think? Are the girls identical or fraternal? We should know the results in a week or two, so I'll let you know what we find out!