Are twins becoming way more common, or is it just us?

If you stay up to date on celebrity news as much as we do, you’re probably aware that there’s a serious baby boom going on in Hollywood right now.

And several stars aren't just having one baby, either: Beyonce blew fans away last week when she announced on Instagram that she and Jay Z are expecting twins.

And multiple sources have also confirmed that George and Amal Clooney are expecting twins, too.

Plus, Pharrell and his wife recently welcomed triplets, his rep confirmed to CNN in late January.

What’s going on here? Experts say there could be a few factors at play, and a lot has to do with women waiting longer to have babies.

“As a society, we are having babies later in life which increases the need for fertility treatment,” says Allison K. Rodgers, M.D., a board-certified reproductive endocrinologist at Fertility Centers of Illinois. And that increases the odds that a woman will have multiples (meaning, twins, triplets, or more).

As an FYI, Beyonce is 35 years old and Amal Clooney is 39, though it's unknown whether either woman went through fertility treatments.

That being said, more than 40 percent of babies who are born thanks to help from in-vitro fertilization (IVF) are multiples, according to a study published in the journal Fertility and Sterility.

And, an estimated 36 percent of recent twin births and 77 percent of births of triplets or more in the U.S. were from women who underwent medically-assisted pregnancies, the New York Times reports.

Christine Greves, M.D., a board-certified ob/gyn at the Winnie Palmer Hospital for Women and Babies, says that the identical twin rate has not changed (it’s about four per 1,000 births), but the fraternal twin rate (meaning, a woman has two babies from two different eggs) has increased.

Despite the numbers, Jennifer Hirshfeld-Cytron, M.D., an ob/gyn and reproductive endocrinologist at Fertility Centers of Illinois, says that doctors are increasingly being encouraged to transfer just one embryo in a single round of IVF to lower the odds that women will have multiples.

However, it still happens, and it often has to do with a woman’s age.

“There are guidelines that help us know which age group would do better by putting back one vs. two,” says reproductive endocrinology and infertility specialist Jane Frederick, M.D., medical director of HRC Fertility in Orange County, Calif.

For patients under the age of 35, she typically will transfer one embryo, while she might recommend two embryos for those who are closer to 40.

“The older embryos don’t implant as often,” she explains. “Putting two in doesn’t guarantee twins, but it happens.”

However, Susan Murrmann, M.D., an ob/gyn at McDonald Murrmann Women’s Clinic, says that IVF isn’t the only fertility treatment that can increase a couple’s chance of having twins.

Clomid, an oral medication that stimulates ovulation, can also up your odds of multiples, she says. So can injection medications that are used with insemination (where doctors take a man’s sperm and place it inside a woman’s uterus when she’s the most fertile)—those have a 30 percent rate of resulting in twins, says Hirshfield-Cytron.

Greves says that a woman’s risk of conceiving multiples also increases as she ages, even if she doesn’t use reproductive assistance.

Here’s why: As we age, our bodies produce a higher concentration of a hormone called follicle-stimulation hormone (FSH), which stimulates the development of ovarian follicles.

The more stimulated your follicles, the higher your odds of releasing more than one egg at a time and having multiples.

Women are not typically encouraged to try to have more than one baby at a time, says Philip Chenette, M.D., a board-certified specialist in reproductive endocrinology and infertility at Pacific Fertility Center San Francisco.

“Carrying a baby one at a time, a singleton pregnancy, is far safer for both mother and baby,” he says, noting that risks of complications are between three and 10 times higher with multiples vs. singles.

“The problems that result from multiples are not small issues and can have long-lasting impacts on the mother, her children, and the developing family,” he says, citing preterm birth, low birth weight, pre-eclampsia, diabetes, fetal death, and maternal death as potential issues.

It’s unlikely that we’ll continue to see an explosion of twins and triplets in the future.

“The rate has leveled off in the last two to three years now that infertility specialists are encouraged to implant fewer embryos,” Murrmann says.

“This also can explain why there has been a decrease in the number of triplet births in the past several years.”