According to the US Centers for Disease Control and Prevention, the twin birth rate rose 2% in 2013 (33.7 per 1,000 births). As a mom with twins on the way, you could say I’ve become a bit obsessed with knowing everything there is to know about twins. Whether or not you have multiples in your family, you’ll find these facts about twins fascinating!
1. Surprising factors can increase your chance of conceiving twins
Genetics play a role (a mother who is a fraternal twin herself has four times higher chance of producing twins), but other factors increase your chances too, including your age—moms over 30 have greater chance of releasing more than one egg at ovulation. Height is also a factor. Taller women have more insulin-like growth factor (IGF) which results in increased sensitivity of the ovaries. In addition, moms who are breastfeeding when they get pregnant are 9 times more likely to conceive twins (even if you’ve weaned but breastfed for over 20 months, you have a higher chance for twins). And finally, diet. Women who consume dairy may be up to five times more likely to conceive twins than a vegan.
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2. Many parents worry about telling their identical newborns apart
If there’s no easy distinguishing factor (such as size, birthmarks, cowlicks or moles), some take to painting a toenail in an identifying color, using infant-safe jewelry, or color coding wardrobes. Once the umbilical cords fall off, their belly buttons can be a giveaway.
3. Twins have been shown to begin interacting in the womb as early as 14 weeks
This makes sense when you think about the special bond twins seem to have!
4. Timing is everything.
Identical twins are the result of one egg splitting post-fertilization, but the timing of the split determines if the twins will each have their own sacs and placentas (split on day 1-3, called di/di twins), share a placenta (split on day 4-8, called mo/di twins), share an amniotic sac and placenta (split on day 8-13, called mo/mo twins) or be conjoined (split on day 13-15) which is, of course, the most rare: only 1 in 200,000 births.
5. One twin can be getting more nutrients than the other
When identical twins share a placenta and one twin gets more nutrients and blood volume than the other it results in Twin to Twin Transfusion Syndrome (TTTS). It can happen at any point in the pregnancy and can result in the death of one or both twins. There are treatments available, so frequent exams and ultrasounds are necessary to keep an eye on the situation.
6. A lot of times the only way to tell if twins are fraternal or identical is a test
If they are boy/girl, they are fraternal. If they share a placenta or amniotic sac, they are identical (unless they had two placentas that fused together, which is possible). Other than that, you’ll have to wait until they’re born! However, fraternal twins may look identical, so the only way to be sure is to do the Zygosity genetic testing, which is via a simple swab of the cheek. Knowing whether twins are identical or fraternal is not just to satisfy your curiosity, but it can help knowing in certain health conditions.
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7. Identical twins have nearly the same DNA
Identical twins have DNA that is 99.9% the same. They also have almost nearly identical brain wave patterns. But they do have different fingerprints and teeth marks!
8. Twins have a higher rate of left-handedness
22% of twins are left-handed as opposed to the 10% of singletons who turn out to be left-handed.
9. You can eat your twin
An estimated 1 in 8 pregnancies begins with twins with only 1 in 70 actually producing twins. This is because of “Vanishing Twin Syndrome” where one of the babies doesn’t survive. This is usually early on and the embryo is reabsorbed by the mother’s body or by the surviving twin causing no issues for the remainder of the pregnancy.
10. Twins can have different birthdays
While it’s extremely rare, it’s possible to birth one twin days, weeks, or even months before the other! The current record is twins born 87 days apart (the first twin was born 4 months premature).
11. The highest rate of multiple births is in Nigeria
About 4% of births in Nigeria are twins (as of 2008) whereas China’s, one of the lowest, is about 1.1% (as of 2011). Within the US, Massachusetts has the highest rate of twin births (4.5 per 100 births) with the national rate being about 3%.
12. The location of the baby in the womb denotes which baby is Baby A and which is Baby B
Baby A refers to the twin located lower in the womb and Baby B refers to the baby that is higher.
13. Twins put you in the “high risk” category but that doesn’t necessarily mean having a C-section.
Many practitioners will agree to try for a vaginal birth if Baby A is head down. Once Baby A is born, Baby B should be able to be born in any position. Most practitioners will require you to deliver in the operating room, just in case you need an emergency c-section.
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14. The average time between delivering the first and second twin is 17 minutes
Most practitioners will induce by 38 weeks. The average birth weight is just 5 pounds 5 ounces (as opposed to the 7 pound 7 ounce average singleton).
15. The rate of identical twins is universal
It’s not impacted by race, nationality or genetics and is about 1 in 285 births. Identical twins do not run in families and they are much less common than fraternal twins.
16. Polar bears most commonly birth twins
They very rarely birth singletons or triplets.
17. About 25% of identical twins are “Mirror Image Twins”
Meaning they are exact reflections of one another. For example, if one has a freckle under the left eye, the other’s freckle will be under the right eye.
18. There is such a thing as half identical twins
It is the result of one egg that splits and then each half becomes fertilized by different sperm. They will share 75% of their DNA.
19. It’s been said that healthier moms have twins
A study in the journal Proceedings of the Royal Society B focused on mothers in the 1800’s and suggested that “Twins could be an evolutionary adaptation in which healthy moms take the chance to pass on double their genes at once.”
20. Twins can have different fathers
It’s extremely rare, but if a woman releases more than one egg and goes on to have intercourse with two different men in her window of peak fertility, it can result in fraternal twins with different dads.
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21. Fraternal twins are no more alike than any siblings
Fraternal twins (i.e. two eggs that got fertilized separately) can look identical or completely different, even having different skin colors. It’s basically a genetic roll of the dice which genes each baby will receive from mom and dad (just like with singletons).
22. Forty percent of twins develop their own language
It can happen when any similarly aged babies are around each other a lot and developing language skills at the same rate. This made-up language usually disappears once the babies learn a real language that allows them to communicate with others.
23. Say two sets of identical twins married each other…
Their children would technically be cousins but the cousins would have the same genetic closeness as the actual siblings.
24. Celebrities have twins, too
Scarlett Johansson has a twin brother, Kiefer Sutherland has a twin sister, Ashton Kutcher has a fraternal twin brother with cerebral palsy, Elvis had an identical twin brother who was stillborn, Gisele Bundchen has a fraternal twin sister, Napoleon Dynamite (aka Jon Heder) has an identical twin brother, Isabella Rossallini has a fraternal twin sister, Alanis Morissette has a twin brother, Ashley and Mary Kate Olsen are fraternal twin sisters, Vin Diesel has a twin brother and Tia and Tamera Mowry are identical twin sisters (though they didn’t find out until they took the test at 35 years old!).
25. Twins Day is celebrated in Twinsburg, Ohio every year
This summer (August 7-9, 2015) will be its 40th celebration.
Photo credit: iStock/crysrob
