For women planning to have children, one unavoidable number is 35.
Giving birth at or beyond this age labels you as being of “advanced maternal age.” This term is a modern, gentler substitute for the older term: “geriatric pregnancy.”
According to fertility experts, many women see age 35 as a critical threshold. Beyond this point, it’s believed that conceiving and carrying a pregnancy to full term becomes significantly challenging.
This perception is widespread, but it’s not entirely accurate.
The idea of a “fertility cliff” has taken hold, especially in the American mindset, since the 1970s, says Emily Mann, a sociologist at the University of South Carolina.
“It’s become a buzzword,” she added.
Despite this, more women over 35 are becoming pregnant. Data from the Centers for Disease Control and Prevention released in July shows that while the general US fertility rate dropped in 2024 to 53.8 births per 1,000 women of reproductive age, the birth rate among women aged 35 to 39 remained stable. Furthermore, the birth rate for women over 40 increased by 2%.
This trend may partly result from changing economic and social factors. Many women delay pregnancy due to financial constraints, educational commitments, or the search for the right partner. Advances in reproductive technologies, such as in vitro fertilization, have also enabled more women to conceive later in life.
“It’s generally easier for younger women to conceive than older women,” Mann noted. “But that’s based on population data and doesn’t necessarily predict individual experiences.”
Age is the primary factor influencing infertility. “That’s undeniable,” stated Dr. Francesca Duncan, an associate professor of obstetrics and gynecology at Northwestern University. Infertility is typically defined for those under 35 as not conceiving after a year of trying.
However, fertility doesn’t abruptly decline at 35. It’s influenced by a complex range of factors affecting both women and men.
Why is 35 often seen as the turning point?
Historically, 35 was the age when the risk of a fetus having a chromosomal anomaly equaled the risk of miscarriage from amniocentesis, a procedure detecting such anomalies.
“This notion of 35 as a magic number has persisted,” said Duncan.
The likelihood of pregnancy complications increases with age, and after 35, this risk escalates sharply. The annual risk increase is greater in the late 30s compared to the mid-20s, according to Dr. Natalie Clark Stentz from the University of Michigan Health.
Fertility outcome data varies. The American College of Obstetricians and Gynecologists states that healthy couples in their 20s or early 30s have a 25% to 30% chance of conceiving each menstrual cycle. By age 40, this chance drops below 10% per cycle.
How does a woman’s fertility evolve with age?
— Egg reserves decline, and quality diminishes
Women start life with a finite number of eggs — about 1 to 2 million — which decrease over time.
The American College of Obstetricians and Gynecologists notes that women’s peak reproductive years are from late teens to late 20s. As they reach their mid-30s, the rate of egg loss accelerates. By 37, women typically have about 25,000 eggs left.
The speed of egg depletion varies individually. Factors like smoking and metabolic conditions such as obesity and diabetes can hasten this decline.
Genetic influences on egg reserves are under study. If a woman’s mother gave birth at 40, it doesn’t guarantee her own fertility at that age, but it might increase her chances, Stentz explained.
Egg quality also impacts fertility, deteriorating as women age.
— Hormonal fluctuations
With age, women’s ovaries produce less estrogen and progesterone, complicating conception and leading to menopause.
“Hormonal changes occur every decade,” said Dr. Mary Rosser from Columbia University Irving Medical Center. “These changes reduce fertility.”
— Age-related complications
As women age, they’re more prone to conditions that hinder pregnancy, like fibroids, which are more common between ages 30 and 50.
The risk of diabetes, obesity, and autoimmune disorders, which are linked to infertility, also rises with age.
What about men’s fertility with age?
Less research has focused on male fertility decline. However, as men age, conceiving becomes harder. They produce new sperm lifelong, but by their 40s, testosterone drops and sperm quality worsens. Aging can alter sperm shape, affecting their mobility and fertilization ability.
Like women, older men are more likely to develop chronic conditions like diabetes and hypertension, which can impede conception.
Researchers are exploring behavioral factors affecting male infertility, such as marijuana use.
What now?
Some experts argue that fixating on a specific age can mislead perceptions of fertility care. Women over 35 who can’t conceive after six months should seek an infertility evaluation.
However, the age marker is more historical and practical than biological, Rosser stated.
“I’m surprised that 35 is still viewed as a significant marker,” she said.
This article originally appeared in The New York Times.
