One number is inevitable for women who want to have children: 35. When you give birth at this age or later, doctors will say that you are of “advanced maternal age.” This term is the newer, gentler version of an old designation: “geriatric pregnancy.”
Doctors and fertility researchers say many women view age 35 as a turning point. After that, according to the theory, getting pregnant and continuing the pregnancy becomes very difficult.
This line of thinking is widespread. That’s not entirely true either. The concept of “fertility cliff” has “really established itself, particularly in the American imagination, since the 1970s,” explains Emily Mann, sociologist at the University of South Carolina. “It’s like a buzzword,” she adds.
And yet, more and more women aged 35 and over are becoming pregnant. Data from the Centers for Disease Control and Prevention released in July showed that while the overall fertility rate in the United States fell in 2024 — to 53.8 births per 1,000 women of childbearing age — rates of women giving birth between ages 35 and 39 remained stable. And the rate of women over 40 giving birth increased by 2%, according to the data.
This could be due, at least in part, to changing economic and social trends. More and more women say they are waiting to become pregnant because they cannot yet afford to raise children, because they want to finish school and pay for a degree, or because they want to find the right partner. And as assisted reproductive technologies have improved, more women have sought procedures such as in vitro fertilization, which can help people get pregnant at older ages.
“We know that it’s generally very easy for a younger woman to get pregnant than an older woman,” Mann says. “But this is population-level data. It doesn’t necessarily indicate, as an individual, how difficult or easy it might be.”
Age is the main factor causing infertility. “There’s no denying it,” says Francesca Duncan, associate professor of obstetrics and gynecology at Northwestern University. Researchers generally define infertility in people under 35 as not getting pregnant after a year of trying.
But fertility doesn’t suddenly drop on your 35th birthday. It depends on a complex series of factors, for both women and men.
Why has 35 become a not-so-magic number?
Historically, 35 was the age at which doctors determined that a woman’s risk of having a fetus with a chromosomal abnormality was roughly equal to her risk of having a miscarriage after an amniocentesis – a procedure to detect some of these abnormalities. “It kind of set 35 as this magic number,” Duncan says.
The risk of having a pregnancy with a chromosomal abnormality or miscarriage generally increases with age. But after age 35, this risk intensifies. The annual increase in risk is much greater in the mid-to-late 30s than in the mid-20s, says Natalie Clark Stentz, medical director of the Center for Reproductive Medicine at University of Michigan Health.
Data on fertility outcomes vary. According to the American College of Obstetricians and Gynecologists, a woman’s chance of getting pregnant in a given menstrual cycle is about 25 to 30 percent for healthy couples in their 20s or early 30s. At age 40, a woman’s chance of getting pregnant is less than 10% per menstrual cycle.
Egg supplies are decreasing and quality is deteriorating
Women are born with a set number of eggs – around 1 to 2 million – which die as they age.
The American College of Obstetricians and Gynecologists states that a woman’s peak reproductive years are between the late teens and late 20s. As women approach their mid-30s, they lose their eggs faster and faster each year. At age 37, women have around 25,000 eggs left.
Hormonal changes
As women age, their ovaries gradually produce lower levels of estrogen and progesterone, making it difficult to conceive and ultimately leading to menopause.
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 pregnancy difficult. For example, fibroids – tumors of the uterus that can cause infertility – are more common in women aged 30 to 50.
The risk of developing diabetes, obesity and autoimmune diseases linked to infertility also increases with age.
What happens to men’s fertility as they age?
Researchers have paid much less attention to how male fertility declines with age. But men also have more difficulty conceiving as they age. Men produce new sperm throughout their lives, but when they reach age 40, their testosterone levels drop and they gradually produce lower quality sperm. And as men age, their sperm can subtly change shape, making it more difficult for eggs to swim quickly and fertilize.
Just like women, men are more likely to develop chronic conditions like diabetes and high blood pressure as they age, which can make it difficult to conceive.
And now ?
Although some researchers say that focusing on a specific age can be misleading, it still affects how we think about fertility care. Doctors recommend that women over 35 who have tried unsuccessfully to get pregnant for six months undergo an infertility evaluation.
Yet this number is a historical and practical marker, not a biological limit, Rosser explains.
“I’m actually surprised that 35 stayed the way they are,” she says.
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