Our twins are di/di (they had two sacs and two placentas - the lowest risk for twins). With di/di twins, many docs and ultrasound technicians (including 2 of mine!) erroneously announce to parents as a matter of factly that they're fraternal. The truth is, if di/di twins are the same sex and blood type, there's only one way to know for sure that they are fraternal: a genetic test!
Actually, 30% of di/di twins are identical, or monozygotic. Here's the timeline of how the different types of identical twins happen: If the fertilized egg splits early enough, in the first 3 days, the babies will go on to develop their own sacs and placentas (di/di twins). If it splits in the next couple of days, they'll have their own sacs but share a placenta (called mono/di). If the split happens in the next few days they'll share a sac and placenta (called mono/mono, which is very high risk). And if the split happens later they will be conjoined twins (extremely rare and dangerous). There are some other interesting things that can happen. For example the egg could split before being fertilized, which results in "half twins". And it can also happen that the two placentas of fraternal twins fuse, making it appear that they share a placenta, in which case they could wrongly be assumed to be identical. Phew! This stuff is crazy complicated, right!??
Anyway, back to our story! When our girls were born, they did look different. They had different skin tone, slightly different facial features, and different colored and textured hair. However, they shared the same blood type and eye color, so we weren't 100% they were fraternal. As the months have passed, some things have gotten more similar and others more different. Right now, Mia has brown eyes and Emi hazel. Their hair is now pretty much the same brown color but Mia has a lot more of it (probably because I picked Emi's cradle cap out along with lots of hair, whoops!)
From what I've read and heard, even "identical" twins can have many differences that result from differences in environment in the womb, and slight genetic changes that can happen after the egg splits. Sometimes they end up with different head shapes, birth marks, hair color, etc! So, every time someone asked us if our girls were identical or fraternal, my answer of "fraternal, we're pretty sure" annoyed myself and probably the inquisitor.
I knew I couldn't live with this uncertainty. I just had to KNOW FOR SURE, you know?? I'd heard about the zygosity test in my Facebook twins group and went ahead and ordered the test through Affiliated Genetics (check out their YouTube video which explains twins and the genetic test really well). It was pretty straight forward. You get some swabs and rub the inside of each baby's cheeks and under the tongue and then press on a grid that absorbs the liquid and cells - you have to do this 4 times per baby (luckily the girls didn't protest).
We mailed in the tests and then the hard part... waiting! It took just over 2 weeks but finally the results came. Drum roll please....
OUR TWINS ARE FRATERNAL!!!!!
Without getting too technical (because I don't really understand it much myself), they looked at 15 different STR markers in their DNA and noted whether they were discordant or concordant. Our girls were only concordant on 4 of the 15!!! So, the results were without a doubt that they are dizygotic (fraternal). We're not a bit surprised, but are thrilled to finally know for sure and be able to answer with certainty the bazillion times a day we get asked! HA!!
But it's not just out of curiosity that parents and kids should know their twin status... if twins are monozygotic, it's very likely they will share most medical issues. They will also be an exact blood and organ donor match for each other. Fraternal twins, on the other hand, are no more similar than any siblings (siblings who just happened to share a womb and birthday). They will have an increased chance / risk (depends how you look at it LOL) for having fraternal twins themselves, though! That's because hyperovulation can be genetic and passed down (it "skips" generations with sons, since they don't ovulate obviously, but they will pass the gene down to their girls).
There are other things that increase your risk of ovulating more than one egg at a time, including IVF and fertility drugs, but also the following (which were all in play for me): increased maternal age (the eggs are having a going out of business sale and jumping ship 2 or 3 at a time), being a dairy drinker/eater, being tall, and practicing extended breastfeeding or having recently weaned. Because my husband and I have ZERO history of twins on either side of our families, it's not likely my hyperovulation was genetic, but it's possible I've started the trend. We'll see! Maybe I'll get a whole bunch of twin grandbabies in about 30 years!!! How fun!
Now that we've gotten our feet wet with this whole genetic testing thing, I'm really interested in doing an ancestral / ethnicity test for all 5 of us. It breaks down what percents you are (again, noooooo idea how this actually works, but I love the idea of it!). Our son Kenzo looks pretty much half Asian and half caucasian, but our girls don't look very Asian at all (yet?). It would be really interesting to see if their blood shows them as not having gotten much of the Japanese DNA! Maybe my husband would like to throw in a paternity test while we're at it, LOL!!!!
UPDATED: We actually did find out our ancestry with 23andMe - check out that blog post here or watch the video below!
Here are some related posts you may enjoy:
We're Pregnant... With Twins!!!
How To Prepare for Having Twins
My Positive Twin Birth Story
Disclaimer: Although I did receive this product and service free of charge, all thoughts and opinions are my own and completely unbiased.
About Me ^_^
I'm a NYC metro area mom blogger living in NJ with my Japanese husband & our 3 kids (twins plus 1). This blog is chock full of product reviews, family travel guides, and giveaways galore! It's also home to Bay Ridge Families, and several guides focused on kid-friendly activities and guides to South Brooklyn, Hudson Valley, and New Jersey, as well as family-friendly destinations beyond the NYC area (check the menu bar!)