5 Things You Didn’t Know About Identical Twins

Learn 5 things that you didn’t know about identical twins from a mom of twins, including identical twin pregnancy information.

Every parent of twins knows what it’s like to be constantly bombarded by questions from strangers. When my boys were babies, I couldn’t buy a gallon of milk without a dozen comments. It’s lessened as they’ve gotten older, but the draw is still there. People are fascinated with twins. The first question, of course, is always, “Are they twins?” A close second is “Are they identical?” When I answer yes, most people have even more questions. While this makes running errands a bit complicated at times, I realize I also didn’t know much about twins before I became a mom to identical twin boys. I learned a lot about the difference between identical and fraternal twins during my high-risk pregnancy and as time passed I found myself learning a few fun facts about multiples. Here are five things you may not know about identical twins:

1. Some identical twin pregnancies are more high-risk than others.

Many identical twins share a placenta in the womb, which puts them at risk for Twin-to-Twin Transfusion Syndrome (TTTS). TTTS occurs when one baby receives too much blood and the other too little. Twins at risk of TTTS must be closely monitored to make sure both babies are healthy and growing. For me, this meant I saw a specialist in addition to my normal OB. I had ultrasounds every two weeks, and sometimes more frequently if anything looked worrisome (I have enough sonograms to create an entire photo album!) Thankfully my boys did not develop TTTS, but it was a constant concern. Many people like to joke and say I got “two for the price of one”, but it was a difficult pregnancy — I got two for the price of two!

2. Identical twin pregnancies aren’t because of genetics.

My least favorite question is, “Do twins run in your family?” I’ve resigned to the fact that I will continue to answer this question until the day I die, but I wish I had a quick answer to give. No, twins don’t run in my family. In fact, identical twins don’t run in families at all. I’m sure there are some families out there with multiple generations of identical twins, but it doesn’t have to do with genetics. Having fraternal twins, however, can be hereditary.

The difference between identical and fraternal twins occurs during conception. Identical twins form when one embryo splits after fertilization. Since embryo splitting is a random event that happens by chance, it doesn’t run in families. Genes are not involved. The same is not true for fraternal twins. Fraternal twins are two different eggs each fertilized by different sperm, which is why they are just as similar in DNA make-up to other siblings as their twin. Most women only ovulate one egg at a time, but some women have genes that make them more likely to release two eggs, hence more likely to have fraternal twins. Genetics isn’t the only factor that plays into fraternal twins, but it can certainly play a part! Unfortunately, that’s a lot of information to pass along to a stranger at the grocery store, but hey, they asked.

3. A small number of identical twins are mirror image twins.

Some identical twins have reverse asymmetric features, like a birthmark on opposite sides of their body. I hadn’t heard of this until my mom brought it up after noticing my boys’ hair whorls are opposite. I looked it up and sure enough, it’s a real thing! About 25% of identical twins are mirror image twins. Some common features that might be opposite include freckles, dimples, and ear shape. In extreme cases, even internal organs can be in opposite locations (this is very, very rare). In addition to physical features, they can also have opposite preferences for certain gestures or movements. One of my boys prefers to use his right hand and the other his left. Now I have a couple tips to share with family and friends who have trouble telling them apart!

4. Identical twins do not have identical fingerprints.

You may think since identical twins share the same DNA, they share the same fingerprints. However, fingerprints aren’t only based on DNA. Identical twins start out with the same fingerprints in the womb, but during weeks six through thirteen of the pregnancy the babies begin to move and touch the amniotic sac, creating different patterns in their fingerprints. My twins are already switching identities at two-and-a-half, so I’m glad there’s another tangible way to tell them apart!

5. Identical twins are alike — and different.

I am often asked, “Are they alike? Or do they have different personalities?” My answer is yes to both. They share common interests and have similar quirks, but they are very different. I noticed this early on as they began hitting milestones at different times. One was sitting, pulling up, and walking before the other. At times, I worried about the other twin, wondering if something was wrong. In reality, there was absolutely nothing wrong with his developmental pace. It can be difficult not to compare them, but I’ve learned they like to move at their own speed. The twin who took longer to walk was quicker to talk and is still slightly more articulate than his brother.

As they’ve grown, their personalities are more and more distinct. One is more mischievous, while the other chases after him yelling, “No! Stop it!” They both love reading books, but one can sit on my lap for half-an-hour while the other lasts ten minutes. They have different food preferences, they respond to discipline in different ways, and sleep for very different lengths of time. One is friendly and quick to give a smile, while the other takes longer to warm up to people. Of course, they fight over the same toys, but most of the time they are okay with wearing different clothing and I prefer to dress them differently anyway (it’s much easier to tell people one is in green and the other is in blue). They are truly unique, but they share such a sweet bond. I love their similarities and their differences.

Allie Mondell lives in Gainesville, FL with her husband and two-year-old identical twin boys.  She has a degree in Mass Communication and occasionally enjoys freelance writing while she’s working as a full-time mom.  When she’s not chasing her twins around, you can find her reading, spending time with her hubby or catching up on some much-needed sleep. You can keep up with Allie on her personal blog.