NEW YORK – There’s an inevitable number for those who want to have children: 35. If you give birth at this age or later, doctors will say you’re of “advanced maternal age.” This term is the newer, weaker version of the old nomenclature: “geriatric pregnancy.”
Fertility doctors and researchers say many women consider age 35 a turning point. After this age, according to theory, getting pregnant and carrying the pregnancy to term is very, very difficult.
This line of thinking is widespread. But this is not entirely true.
The concept of the “fertility cliff,” according to Emily Mann, a sociologist at the University of South Carolina, “has actually been entrenched, especially in the American imagination, since the 1970s.”
“It’s like a buzzword,” he added.
However, more and more women age 35 or older are becoming pregnant. Data released by the Centers for Disease Control and Prevention in July showed that although the total fertility rate in the United States would decline in 2024 — with 53.8 births per 1,000 women of reproductive age — rates for women giving birth between the ages of 35 and 39 remained stable. Birth rates for women over the age of forty increased by 2%, according to the data.
This may be due, at least in part, to changing economic and social trends. Increasing numbers of women say they are waiting to get pregnant because they cannot yet afford to raise children, or because they want to finish their studies and pay for a university degree, or because they want to find the right partner. As assisted reproductive technologies improve, more women are turning to procedures such as in vitro fertilization, which can help them get pregnant at an older age.
“We know that it’s generally easier for a younger woman to get pregnant than an older woman,” Mann said. “But this is population-level data. That doesn’t necessarily tell you, as an individual, how hard or easy it is.”
Age is the main factor that determines infertility. “This is indisputable,” said Francesca Duncan, MD, assistant professor of obstetrics and gynecology at Northwestern University. Researchers usually define infertility in people under 35 as not getting pregnant after trying for a year.
But fertility doesn’t suddenly decline when you turn 35. It depends on a complex series of factors, for both women and men.
Why did 35 become a non-magical 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 miscarriage after amniocentesis, a procedure that can detect some of these abnormalities.
“It seemed like 35 was that magic number,” Duncan said.
The risk of pregnancy with a chromosomal abnormality or miscarriage usually increases with age. But after the age of 35, this risk increases. The year-over-year increase in risk is much greater in the mid-to-late 30s than in the mid-20s, said Natalie Clark Stentz, MD, medical director of the University of Michigan Health Center for Reproductive Medicine.
Data on fertility outcomes vary. According to the American College of Obstetricians and Gynecologists, the chance of a woman becoming pregnant in one menstrual cycle is between 25 and 30 percent, in healthy couples between the ages of 20 and 30. By age 40, a woman has less than a 10 percent chance of getting pregnant with each menstrual cycle.
How does a woman’s fertility change with age?
Women are born with a set number of eggs – approximately one to two million – which die with age.
The American College of Obstetricians and Gynecologists states that a woman’s peak fertile years are between her late teens and late twenties. As women approach their mid-30s, they lose eggs more quickly each year. By age 37, a woman has about 25,000 eggs remaining.
But how quickly those eggs are consumed varies from person to person. For example, chemicals in cigarette smoke can speed up the rate at which women lose eggs. Metabolic disorders such as obesity and diabetes can also contribute to low reserves.
Researchers are increasingly studying the influence of genetics on egg reserves. If a woman’s mother gives birth at age 40, for example, that doesn’t guarantee that she can also get pregnant at that age, but it can increase the likelihood of pregnancy to some extent, Stentz said.
Egg quality also affects fertility. As a woman gets older, the quality of her remaining eggs declines.
Hormonal changes
As a woman ages, the ovaries gradually produce lower levels of estrogen and progesterone, making pregnancy more difficult and eventually leading to menopause.
“Every decade, your menstrual cycles change,” said Mary Rosser, MD, director of comprehensive women’s health at Columbia University Irving Medical Center. “Hormones change, and this can also reduce your fertility.”
Other complications related to aging
The older a woman gets, the more likely she is to have a number of other conditions that can make pregnancy more difficult. For example, fibroids — tumors in the uterus that can cause infertility — are more common in women ages 30 to 50.
The risk of diabetes, obesity and infertility-related autoimmune diseases also increases with age.
What happens to men’s fertility as they age?
Researchers have paid much less attention to how men’s fertility declines with age. But men also have difficulty conceiving as they age. Men produce new sperm throughout their lives, but when they reach age 40, their testosterone levels decline and they produce progressively lower quality sperm. As men age, the shape of their sperm can change subtly, making it harder for them to swim quickly and fertilize eggs.
Like women, men are more likely to develop chronic diseases such as diabetes and high blood pressure as they age, which can make pregnancy more difficult.
Scientists are learning more about behavioral factors that can contribute to male infertility, including:
Now what?
Although some researchers say focusing on a specific age can be misleading, it still influences the way we think about fertility care. Doctors recommend that women over the age of 35 who have tried to get pregnant without success after six months undergo an infertility evaluation.
Rosser said this number remains a historical and practical milestone, not a biological limit.
“The truth is, I’m surprised 35 people stay like this,” he said.