If you’ve looked around lately, it might seem like everyone is having twins, from Hollywood celebs (hey, Beyoncé and Amal) to the lady down the street. Is there something in the water? Could you be next?
Before you start looking at double strollers, here’s what you need to know about your chances of having twins.
What are the odds of having twins?
To keep it in perspective, not everyone is having twins. According to the Centers for Disease Control and Prevention (CDC), in 2016 there were 33 twin births for every 1,000 births in the United States. For every 1,000 births, one of them was triplets or higher multiple births.
The numbers show a steady increase in twin births over the years, with the peak occurring in 2014, but the same can’t be said for triplet or higher multiple births. That number has actually lowered over the years. According to the National Vital Statistics System, the number of triplet or higher-order births was down to one in 880 births in 2014 from about one in 515 births in 1998.
How do twins develop?
OK, so there are two types of twins. Are you seeing double yet? Identical twins, also known as monozygotic twins, happen when a single egg is fertilized by a single sperm but then separates into two embryos. The embryos will share the same placenta and chorion (the outermost fetal membrane that surrounds the embryo), but when the fertilized egg splits determines if there will be two different amniotic sacs, a shared outer sac and two inner sacs, or the same two sacs. Fraternal twins, also known as dizygotic twins, occur when two eggs are fertilized by two different sperm. Each embryo will have its own placenta, amniotic sac and chorionic sac.
What factors can increase my chances of having twins?
There’s definitely nothing in the water that you have to worry about, but there are some factors that can make it more likely for you to have multiples.
1. Family history
Look at your family tree: Are there any “double” branches, so to speak? If so, you could be adding two more. “If there is a history of fraternal twins on the mother’s side only, there is an increased chance of having twins,” says Candice Wood, an OB-GYN at Banner University Medical Center in Phoenix, Arizona. If there are only identical twins, your chances of having twins are still elevated but not as high, she says.
It’s no secret that women are waiting longer to have kids. In 2017, the average age when a woman had her first child was 28, according to the latest data from the CDC. That’s up from age 24 in the 1970s. The older you are, the more likely you are to have twins. When you’re 35 or older, you actually produce more follicle-stimulating hormone (FSH), which is what causes the egg to mature each cycle. That extra FHS may actually cause you to release more than one egg in a single cycle. “When you get older, it’s harder to get pregnant, but twinning is higher,” says Wood. Because a woman’s chances of getting pregnant decline later in life, many older women turn to fertility treatments, which also increase their chances of having twins.
3. Fertility treatments
Fertility drugs typically work by increasing the number of eggs that a woman’s ovaries produce. If you take the in vitro fertilization route, your chances of having multiples depend on how many eggs are being implanted, says Wood. It is very uncommon for triplets or higher-order births to happen naturally. These typically occur with some type of fertility treatment.
According to Johns Hopkins Medicine, African American women are more likely to have twins than any other race. Caucasian women, especially those over the age of 35, have the highest rate of higher-order multiple births (triplets or higher). Asian and Native Americans have the lowest rates of twin births.
If you’re tall, you’re more likely to have twins. “It’s not known why,” says Wood, “but taller females have an easier time carrying twins.” One theory proposed by Gary Steinman in a 2006 study in The Journal of Reproductive Medicine is that taller women (five foot five or taller) have more insulin-like growth factor (IGF), which increases the sensitivity of the ovaries to FHS and results in them potentially releasing more than one egg each cycle.
6. Previous pregnancies
Are you getting ready to have baby number two or three? Then you’re more likely to have twins! According to Johns Hopkins Medicine, having one or more previous pregnancies increases your chances of having multiples.