8 Things You May Not Know About Identical Twins

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We all know they’re super cute, but there may be some things you don’t know about identical twins. As a mom of identical twins I am repeatedly asked many of the same questions, and often people are about the difference between identical and fraternal twins. Here are just a handful of geeky and fun facts about identical twins to get you thinking.

Things you may not know about identical twins pin

1. Identical twins are not hereditary. 

Fraternal (non-identical) twins are caused by the release of multiple eggs from the mother’s ovaries and therefore she conceives multiple times at once. The tendency to hyper-ovulate is passed on from generation to generation, although there are other factors such as age that play a part here. On the flip side, identical twins are essentially fertilization gone wrong (sorry twinkies)… No one knows what causes that tiny fertilized egg to split, essentially cloning the conceived child (although there are theories). It is one of those freak-of-nature events that can happen to anyone. Yes, anyone… no one is safe here people, it could be you.

sciency source: verywell.com

2. The chances of having them is 0.3%.

The chances of conceiving twins has risen considerably in the last 30 years. In fact the rate has risen from 2% to 3.3% of babies being born a twin. This is likely due to moms wanting babies later in life, where the chances of releasing multiple eggs is higher (your body’s natural way of trying to increase the chance of conception while getting closer to menopause). However, the rates for conceiving identical twins have not changed… It has stayed steady at 0.3%. What lucky freak moms we are!

sciency source: theatlantic.com

chances of having identical twins

3. People are obsessed with them. 

Prepare yourself to become an instant celebrity as soon as you leave the hospital. Plan an extra 20mins on your grocery store run and prepare to answer the same questions again and again. On an average trip to the shops I am stopped around five times… Not only are people super excited just to see two babies that look the same, but they will all have a set of twins somewhere in their family they will insist on telling you about. And occasionally you come across an adult twin… They go nuts for it! People are literally obsessed with the science and the cuteness and everything in between. And of course there is all the freaky horror movies…

4. They don’t have identical fingerprints.

I’m pretty sure there are a number of crime dramas that use this nugget of knowledge in their screenplay… A basic DNA test will not identify ‘who done it’, but if the criminal was careless enough to leave a print at the crime scene it’s all over. This is because the formation of fingerprints is semi-random (I know… What does that even mean?!) and are influenced by chance fluctuations in hormones which would be different for each child. This also goes for the position of freckles – these are random mutations and are therefore different for each child.

sciency source: sciencefocus.com


5. They are often born very different sizes. 

A pregnancy with babies sharing a placenta is considered ‘high-risk’ because there is the chance of Twin to Twin Transfusion Syndrome. The size of your babies will depend partly on how much oxygen and nutrients they are receiving from the placenta, and occasionally one gets greedy and takes more than their equal share, leaving the other a little behind in growth. It is very normal to have a slight size difference, and unless the discordance goes beyond 20%, it doesn’t tend to cause a problem. Growth of twins is frequently monitored, and don’t panic, we live in the 21st Century and there are things doctors can do to remedy severe cases such as placenta laser surgery (I know… sounds terrifying) and delivering a little early.

sciency source: tttsfoundation.org

6. They don’t always share a placenta. 

Whether or not identical twins share a placenta and an amniotic sac is dependent of when exactly the fertilized egg splits. If it happens during day 1 after fertilization they will form separate placentas and amniotic sacs. However, it is more likely the split with occur around day 4-5 they will have time to form separate sacs but will end up sharing a placenta. 1% of the time the split happens at day 9-10 meaning the babies end up sharing a sac which can cause complications with the little ones getting wrapped up in each others umbilical cords. And lastly, if your embryo decides it wants a clone buddy around day 13-15 they are unable to separate fully, causing the babies to be born conjoined.

sciency source: usatoday.com

facts about identical twins

7. They won’t necessarily like the same food. 

This is where the nurture/nature thoughts start to explode your mind, and as a mother of twins I can say it baffles me everyday. Genetic clones, these babies should have identical taste buds and therefore enjoy the same flavors… right? But alas, the first food I offered my boys was banana – one liked it, the other didn’t. Butternut squash – a hit with one, the other is not impressed. Outside influences are supposed to make the difference here (the nurture) and once the kiddos get older they may start to oppose each other on purpose to enhance their individuality – french psychologist Rene Zazzo called this twin phenomenon ‘The Couple Effect’. Personally, when 4 month-old babies treated the same show different tastes I’m not really buying either. I like to think its a difference in the soul… OK I’m getting all fluffy now.

sciency source: christinabaglivitinglof.com

8. They might be mirror twins.

Mirror image twins are a subset of identical twins, occurring when the fertilized egg splits between day 7-12, and is characterized by asymmetries of the body being on opposite sides. For example, one may be right handed while the other prefers the left. One may have a birth mark on their left cheek while the other has a matching one on their right. Partings in their hair, or asymmetries of their teeth, it can all be mirrored, and in extreme cases can be seem in organ positions and skeletal features – we’ve all seen Orphan Black, right?

sciency source: twin-pregnancy-and-beyond.com


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About the author

Katherine is an electrochemist, hiking enthusiast, and family lifestyle blogger. As a mom of three, including twins, she enjoys DIY, travel, and eating good food. British born, Katherine moved to the US in 2014, and now called Las Vegas home.

25 thoughts on “8 Things You May Not Know About Identical Twins”

  1. That’s really interesting – I had no idea about most of those things, especially that twins aren’t hereditary! I have so much respect for parents of twins – I struggled with one infant, so I literally can’t imagine managing two at the same time. Hats off to you. #EatSleepBlogRT

    • It’s only the identical variety that are not hereditary, fraternal twinnies do indeed run on the Family! I think we all struggle whether it’s one or two, babies are tough!

  2. I enjoyed reading this – I’ve been a Midwife then a Neonatal Nurse for 30 plus years. Now Ultrasound scans identify if twins are identical or not. When I first started in my roles scans were not sophisticated and the only way you’d know was if the midwife at delivery could inspect the placenta and membranes closely enough to see how many layers to the membranes – if not parents just had to wait and see!

    • I was actually a bit of a wait and see because with moving house (and doctor) I missed the optimum time to tell. Therefore they couldn’t tell if I had one giant placenta or too smaller ones pushed up against each other. They treated me as high risk anyway and sure enough, that mono-di placenta popped out!

    • Mine are slowing becoming less identical, mainly because one loves his fruit and veg and the other is a carb monster… resulting in slightly different frames ?

  3. #eataleepblogrt I am the woman in the supermarket that asks a thousand questions. So I loved this article as it hit home with some fab facts (that I’ll tell the next twin parent in the supermarket)

  4. Twins are the only people in the world who can have identical vocal cords. My sister and I do — even her children can’t tell us apart when we speak. The awe they had when they first heard us sing a Christmas carol together!! My mom always teased we were “in stereo” whenever we said things at the same time. Which happens when someone asks us both a question.

    • That’s so cool! I can totally see this being the case with singing but with talking there are often differences. My daughter used to go to school with identical twins and the only way she could tell them apart was their voice. I suppose when we talk there are mannerisms to take into account. Can’t wait for my boys to be old enough to test out the singing!

  5. My daughter-in-law is pregnant with identical mono Di twin boys. She is also a mono Di twin, as well as her first cousins. I have found very few cases online where this has happened. Her mother’s side of family have many sets of identical twins.

    • I’ve heard of a number of cases of recurring identical twins recently, there is definitely so much more research to be done! I suspect it is not random that your family has repeat twins… we will see what science comes up with in the future! ❤️

  6. I dont Believe that they’re not hereditary. We have 5 sets of identical twin males on my mothers side of the family!!! That’s a high number to be coincidental?

    • Wow; that is a lot! I’m with you, I’ve heard too many stories of multiple identical twins, it has to be hereditary!


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