8 things you may not know about identical twins…

We all know they’re super cute, but there may be some things you don’t know about identical twins…

identical twins
My boys at 3 months!

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. It is one of the 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

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 six 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 their’s 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

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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Diary of An Imperfect Mum


  1. Most people don’t know that they are not hereditary, and ask if they “run in your family”. No, we’re just freaks. When my daughter was 20 months old, I had identical twin boys. It was rough (I was 22).

    My least favorite comment when they were little (and they are now adults) was “Oh, my kids are 18 months apart, so it’s basically the same as having twins”. Bite my ass. Bite it so hard. Gee, you’re dumb. It’s not the same AT ALL.

  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!

    1. TwinPickle

      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!

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