First Beyoncé and Jay Z, then Amal and George Clooney. It seems like twin pregnancy announcements are popping up everywhere. According to medical studies, it may not be a coincidence.

The CDC says the twin birth rate has been increasing for the last three decades. In the 1980s, one in 53 pregnancies resulted in twins. Now, the statistic is one in 30.

Doctors say one obvious explanation is the rise in assisted reproductive technologies.

“That can include actual procedures such as in vitro fertilization to help a couple to get pregnant. But also, medications that induce ovulation, such as Clomid,” said Dr. Joey England, maternal fetal medicine specialist at Children's Memorial Hermann and McGovern Medical School at UT Health.

England says the chance of having multiples also goes up when a woman reaches 37 years old.

“That’s because their FSH, or their follicle-stimulating hormone, is a lot higher, so they’re more likely to have double ovulation,” said England.

Studies have also shown there’s a higher chance of having twins if a woman gets pregnant right after stopping birth control pills.

Finally, doctors say there’s evidence the chance of multiple births goes up when a couple is on their 4th or 5th pregnancy.