When my twins were born almost two years ago, they shared the characteristics of being both fraternal and identical twins. They shared one placenta like identical twins, but had separate sacs like fraternal twins. At the time, I had asked the pediatrician whether they were identical or not, and he said it was hard to tell because of the situation. I think he used the term "mono-dizygosity" or something. I wanted to get a DNA test done, but then we got involved in the hustle and bustle of juggling three kids under age 2 and forgot. Until we were discharged from the hospital, we used the tags on their feet to tell them apart: Twin A was Z and Twin B was H. When I got them both home finally, I started noticing the individual characteristics of each twin. Z, the older one, was overall a bigger baby, had a round face, and big eyes, and always seemed to squint a little. H, the younger one, had chubby cheeks, small oriental eyes, and really cute smile. As a mother I had to actually look at their face to tell them apart, and this was important because for the first six months, H. was on a medication and I almost accidentally gave it to Z! Good thing I always double checked before administering the medicine.
As they grow older, they are increasingly starting to look more and more alike. They both have their personal security blankets, or "blankies" as they like to call them, and in the middle of the night when they come waltzing back to my room from their beds, I actually have to look at the color of the blanket to figure out who it is! H has a wild plaid color blankie and Z's is purple. Aside from that, even my husband and I are starting to confuse them. My sister-in-law recently said she always thought the twins were identical, she could never tell them apart and it drove her crazy when I dressed them alike because that further complicated things. My own mother recently admitted that she used to try to remember the clothing color of the day to tell them apart, but when they were dressed alike, it took a while to figure out who was who. Especially since they have the exact same hairstyle. They have different personalities and behaviors so that helps differentiate them, but other than that it's like looking at two identical peas in a pod. Now that they have started talking a little, they are playing even more games with people. Both of them think their name is H. Z knows her name is Z and will respond to Z, but when you ask her "what's your name?", she says "H". And H says her name is "H" as well. It drove my mom nuts one day when she was trying to figure out who was who, and both of them were saying their name was "H".
I continue to insist the girls are fraternal. When they both stand next to each other I can clearly tell the difference, but everyone else who sees them sees identical twins. I finally decided to settle the case once and for all and am going to get the twin zygosity testing done to see if they are identical or fraternal twins. Genetree is a great site, I actually got the recommendation from another mom of twins I met at the park. She had the same problem with the mono-di thing, so she ordered the kit, swabbed the inside of each girls mouth, and sent in the DNA sample. For a fee of $195, she finally got confirmation that her twins were genetically identical even though they looked totally different. She convinced me it's good to know in case the girls ever have any health issues in the future that require that kind of knowledge.
Of course I'm the mom, so I always know who's H and who's Z, as long as I'm looking at their face. In the light. I'm just doing the test to know for sure how different or not different they are.