Why Women Over 35 Are More Likely to Have Twins

If you're in your mid-thirties or beyond and thinking about having kids, here's something fascinating: your odds of having twins are significantly higher than they were a decade ago. According to CDC data, women aged 35-39 have about a 1 in 20 chance of giving birth to twins—that's roughly 5% of all births in this age group. For women in their 40s and early 50s, that rate climbs even higher to approximately 1 in 13 births.

This isn't just a statistical quirk. It's biology doing something unexpected.

The Double Ovulation Effect

Here's what's happening inside the body: as women age, their hormone levels fluctuate more dramatically. Specifically, follicle-stimulating hormone (FSH) increases as the ovaries become less responsive. Sometimes this hormonal surge causes the ovaries to release two eggs in a single cycle instead of one.

Two eggs, two potential embryos, fraternal twins. It's like your reproductive system is hedging its bets.

This explains why fraternal (non-identical) twins become more common with maternal age, while identical twin rates remain relatively constant across all age groups. Identical twins result from a single embryo splitting—a random occurrence that doesn't correlate with age.

The Fertility Treatment Factor

There's another piece to this puzzle. Women over 35 are more likely to use assisted reproductive technologies like IVF or fertility medications. These treatments often stimulate the ovaries to produce multiple eggs or involve transferring multiple embryos, significantly increasing the likelihood of twins.

Between 1980 and 2009, twin birth rates among women 35-39 nearly doubled, and for women over 40, they more than tripled. While some of this increase is natural biology, fertility treatments have amplified the trend.

What About After 50?

Some sources cite twin rates as high as 1 in 9 for women over 50. But here's the critical context: very few women conceive naturally at this age. When pregnancies do occur in this age bracket, they're almost always through donor eggs and IVF, which skews the twin statistics dramatically higher.

So yes, if a woman over 50 becomes pregnant, twins are surprisingly likely—but the pregnancy itself is extraordinarily rare without medical intervention.

The Modern Twin Boom

Overall, twin births have surged in recent decades. In 1980, about 1 in 53 babies born in the U.S. was a twin. By 2014, that rate had jumped to 1 in 29. Maternal age is a huge driver of this trend, alongside advances in reproductive medicine.

Interestingly, twin rates peaked around 2014 and have declined slightly since, likely due to changing IVF practices that now favor transferring single embryos to reduce complications.

The Bottom Line

Age absolutely increases your chances of having twins, particularly after 35. Whether that's exciting news or slightly terrifying depends on your perspective—but either way, it's a remarkable example of how human biology shifts across our lifespan.

Your body at 25 and your body at 38 play by different reproductive rules. And sometimes, those rules involve two babies instead of one.