One number is inescapable for women who want children: 35.
Give birth at that age or past it, and doctors will say you are at “advanced maternal age.” That term is the newer, softer version of an older designation: a “geriatric pregnancy.”
Fertility doctors and researchers say that many women see 35 as a tipping point. After that, the theory goes, getting pregnant and carrying to term becomes really, really hard.
That line of thinking is pervasive. It’s also not totally true.
The concept of a “fertility cliff” “has really taken hold, and especially in the American imagination, since the ’70s,” said Emily Mann, a sociologist at the University of South Carolina.
“It’s like a buzzword,” she added.
And yet more and more women who are 35 and older are getting pregnant. Data from the Centers for Disease Control and Prevention released in July showed that while the general U.S. fertility rate dropped in 2024 — with 53.8 births per 1,000 women of reproductive age — the rates of women who gave birth at age 35 to 39 remained steady. And the rates of women over 40 who gave birth rose by 2 percent, according to the data.
That may, at least partly, be the result of shifting economic and social trends. More women say they are waiting to get pregnant because they can’t yet afford to raise children, because they want to complete their education and pay off the costs of a degree, or because they want to find the right partner. And as assisted reproductive technologies have improved, more women have sought out procedures like in vitro fertilization, which can help people become pregnant at a later age.
“We know that it’s typically really easy for a younger woman to get pregnant compared to an older woman,” Dr. Mann said. “But that’s population-level data. That doesn’t necessarily tell you, as an individual, how hard or easy it might be.”
Age is the main factor that drives infertility. “That’s incontrovertible,” said Dr. Francesca Duncan, an associate professor of obstetrics and gynecology at Northwestern University. Researchers generally define infertility for people under 35 as not getting pregnant after trying for a year.
But fertility does not suddenly plummet on your 35th birthday. It hinges on a complex array of factors — both for women and men.
Why did 35 become the not-so-magic number?
Historically, 35 was the age at which doctors determined that the risk a woman would have a fetus with a chromosomal anomaly was approximately equal to the risk of having a miscarriage following amniocentesis — a procedure that can detect some of those anomalies.
“That kind of stuck as 35 being this magical number,” Dr. Duncan said.
The risk of having a pregnancy with a chromosomal anomaly or a miscarriage generally increases with age. But after 35, that risk intensifies. The year-to-year increase in risk is much higher in the mid-to-late 30s compared to the mid-20s, said Dr. Natalie Clark Stentz, the medical director of the Center for Reproductive Medicine at University of Michigan Health.
Data on fertility outcomes varies. According to the American College of Obstetricians and Gynecologists, the chance that a woman will become pregnant in any single menstrual cycle is around 25 to 30 percent, for healthy couples in their 20s or early 30s. By age 40, the chance a woman will get pregnant is less than 10 percent per menstrual cycle.
How does a woman’s fertility change with age?
Egg reserves drop, and quality degrades
Women are born with a set number of eggs — roughly one to two million — that die as they age.
The American College of Obstetricians and Gynecologists states that a woman’s peak reproductive years are between her late teens and late 20s. As women approach their mid-30s, they lose their eggs faster and faster with each year. By age 37, women have roughly 25,000 remaining eggs.
But just how quickly those eggs deplete varies from person to person. The chemicals in cigarette smoke, for example, can speed up the rate at which women lose eggs. Metabolic conditions like obesity and diabetes can also contribute to declining reserves.
Researchers are increasingly examining the effect of genetics on egg reserves. If a woman’s mother gave birth at 40, for example, that doesn’t guarantee she’ll also be able to conceive around that age — but it may increase the likelihood to some extent, said Dr. Stentz.
The quality of eggs also affects fertility. As women get older, the quality of their remaining eggs decreases.
Hormonal changes
As women get older, their ovaries gradually produce lower levels of estrogen and progesterone, which makes it harder to conceive and eventually leads to menopause.
“Every decade, your cycles change,” Dr. Mary Rosser, the director of Integrated Women’s Health at Columbia University Irving Medical Center. “The hormones are changing, and that’s going to reduce your fertility, too.”
Other complications related to aging
The older a woman gets, the more likely she is to develop a range of other conditions that can make it harder to get pregnant. For example, fibroids — tumors in the uterus that can cause infertility — are most common in women between the ages of 30 and 50.
The risk of developing diabetes, obesity and autoimmune conditions that are linked with infertility also increases with age.
What happens to men’s fertility as they age?
Researchers have paid far less attention to how male fertility declines with age. But men, too, have a harder time conceiving as they get older. Men make new sperm throughout their lives, but as they hit their 40s, their testosterone levels fall and they gradually produce worse quality sperm. And as men get older, their sperm can subtly shift shape, making it harder for them to swim speedily and fertilize eggs.
Like women, men are more likely to develop chronic conditions like diabetes and hypertension as they age, which may make it harder to conceive.
And scientists are learning more about behavioral factors that could contribute to male infertility, including marijuana use.
What now?
While some researchers say the focus on a specific age may be misleading, it still affects the way we think about fertility care. Doctors recommend that women over 35 who have tried unsuccessfully to get pregnant after six months seek an infertility evaluation.
Still, the number is a historical and practical marker, not a biological cutoff, Dr. Rosser said.
“I’m actually surprised that 35 has stayed like it has,” she said.
Dani Blum is a health reporter for The Times.
The post Does the ‘Fertility Cliff’ Really Hit at 35? appeared first on New York Times.
