Scientific facts about twins

Beyoncé is pregnant with twins! The singer and actress, 35, announced the news on Instagram today, posting a photo of her baby bump and writing that she and husband Jay Z “have been blessed two times over.”

Pregnancies with multiple babies aren’t as rare as they once were, but they’re still an uncommon event. So in celebration of the couple’s happy news, here are 10 fascinating things you may not know about twins—identical, fraternal, and otherwise.

Twin births are on the rise

There were 135,336 twin births in the United States in 2014, the latest year for which data is available. That means about 3.4% of all babies born that year were twins—a record high, according to the United States Centers for Disease Control and Prevention.

The twin birth rate has been climbing steadily since 1980, and experts say that the prevalence of in vitro fertilization (IVF) and other assisted reproductive technologies has likely played a role.

Older moms are naturally more likely to have twins

Even without IVF or other fertility treatments, mothers are naturally more likely to have twins as they get older, says Christine Greves, MD, an obstetrician and gynecologist at Winnie Palmer Hospital for Women and Babies in Orlando.

“It may have to do with evolution,” says Dr. Greves. “Women at an older age won’t be able to have babies for much longer, so it makes sense that they’d have more at one time.”

Twins live longer than singletons—and so do their moms

In a 2016 study from the University of Washington, researchers found that identical twins tend to live longer than fraternal twins, and all twins tend to live longer than the general population. “There is benefit to having someone who is socially close to you who is looking out for you,” said study author and postdoctoral researcher David Sharrow, PhD, in a press release. “They may provide material or emotional support that leads to better longevity outcomes.”

There’s good news for moms of twins, as well: In 2011, University of Utah researchers discovered that women who give birth to twins tend to live longer than other mothers. (It’s not because having twins makes you healthier, say the researchers, but that healthier women are more likely to have twins.)