Twins: The Odds of Drawing Two of a Kind

March 06, 2017

how rare are twins

TWINS! How is this possible?! What are the odds? Not too many people know about or even consider the chances of having twins. It always seems like such a rarity until it is actually happening to you. Before having my twins, I could scarcely think of anyone I knew who had them. But after our announcement they seemed to pop up everywhere. It’s the same weird feeling you get when you finally give in and begin shopping for a minivan and everywhere you look people are zipping around town in their Swagger Wagons.

What are the chances of this happening to your typical American family? Let’s get down to the numbers and find out how rare your pair actually is.

Who’s having twins?

The statistics on twin pregnancy can be dizzying, but we’ll try to keep it simple. The most recent twin birth rate reported by the CDC was 33.9 twins per 1,000 births. Essentially this means there is only about a 3% change of a twin pregnancy overall. Surprisingly the chances of a multiple pregnancy event are in a similar risk category as an unplanned pregnancy while on some sort of birth control.

This number has grown substantially from the 18.9 twin births per 1,000 reported in 1980, but in recent years this figure has largely stabilized. As somewhat common as twins may seem to be these days, only about 1 in 250 overall births (or about 0.4%) are identical twins. You are actually more like to date a millionaire than you are to have identical twins. And those who have a triplet or higher order multiple pregnancy are in an even more exclusive circle of moms; only 113.5 per 100,000 births (a little over 0.1% chance). So if you find yourself facing the prospect of identical twins or triplets, then you may as well work those crazy probabilities and head to Vegas. May the odds be ever in your favor indeed.

The rise in twins

So why the rise in twins over the last 40 years? The science indicates that increased use of fertility therapies, to include ovulation-inducing drugs and assisted reproductive technologies (ART), and the older advanced increasing average maternal age (hey, 35 is the new 20) are the biggest contributors to the climb. In fact, 1.5% of births in 2012 resulted from ART. And as to the age factor, women over 30 have increased levels of the hormone FSH (follicle stimulating hormone) which can sometimes contribute to the release of more than one egg per ovulation cycle. Interestingly, ART increases the chances of conceiving both fraternal and identical twins, a fact which researchers are still trying to understand.

Other factors that might affect your chances of having fraternal twins include family history, weight, height, number of previous pregnancies, race, whether you conceived while breastfeeding, and diet. Those with fraternal twins in their families, who are taller and have a higher body mass index (BMI) are more likely to have twins. Higher consumption of dairy is also associated with increased chance of twin pregnancy, which is likely attributable to the increased presence of growth hormones in dairy products.

Interestingly, twin rates differ among races. African-American women are the most likely group to conceive twins, and Asian-Americans and Native Americans are the least likely. If you are feeling a little down about being an older, slightly pudgy dairy addict like I was (damn you delicious cheesy goodness), rest assured that things are not all bad! A University of Utah study found that twin moms are physically exceptional people that tend to live long and healthy lives. You’re welcome.

Do all these statistics have your head spinning? The bottom line is that a multiple pregnancy, while increasingly more common, is still a rare and extraordinary thing. Against all odds, your strong and amazing body will be witness to the miracle of not one but two or more beautiful babies entering this world hand in hand. And that is a special thing.