Maternal age refers to a mother’s age at the time she gives birth or, in some contexts, at the time of conception. While the term itself is straightforward, it carries significant medical weight because a mother’s age influences fertility, pregnancy risk, and the health of the baby. In medical settings, the term comes up most often when discussing “advanced maternal age,” which generally means being 35 or older at delivery.
Why 35 Is the Key Threshold
Although there is no single standardized definition, advanced maternal age (often abbreviated AMA) most commonly refers to being older than 35 at the time of delivery. Beyond that, doctors recognize additional categories: “very advanced maternal age” for women over 40, and “extremely advanced maternal age” for women over 45.
The age-35 cutoff isn’t arbitrary. Population data from England and Wales show that the rate of certain pregnancy complications, including molar pregnancy, steadily declines from the teenage years through the early 30s, then begins rising again at 35. By 40, complications become more frequent, and by 45, they increase sharply. This pattern repeats across many different types of pregnancy risk, which is why 35 has become the standard reference point in prenatal care.
How Maternal Age Affects Fertility
The connection between age and fertility starts with egg supply. A female fetus has roughly 6 to 7 million eggs at 20 weeks of development in the womb. That number drops to 1 to 2 million at birth, 300,000 to 500,000 at puberty, about 25,000 by age 37, and around 1,000 by age 51. The decline accelerates noticeably after 32 and again after 37.
Egg quality matters just as much as quantity. As eggs age, they become more likely to have the wrong number of chromosomes, a problem called aneuploidy. A woman under 25 undergoing IVF needs roughly 5 eggs to produce one chromosomally normal embryo. A woman over 42 would theoretically need around 200 eggs for the same result, which is essentially impossible in a single cycle. This is the core reason fertility drops so steeply in the late 30s and 40s.
Miscarriage Risk by Age
Miscarriage risk follows a U-shaped curve. A large register-based study published in The BMJ found the lowest risk among women aged 25 to 29, at about 10%. Women in their early 30s had a similar rate of roughly 11%. At 35 to 39, the risk climbed to about 17%. By 40 to 44, it reached 32%, and after 45, more than half of recognized pregnancies ended in miscarriage.
The primary driver behind this increase is the same chromosome problem that affects fertility. As eggs age, cell division errors become more common, and embryos with the wrong number of chromosomes are far less likely to survive.
Genetic Risks, Especially Down Syndrome
The risk of Down syndrome (trisomy 21) is one of the most well-documented effects of maternal age. At age 20, the odds are about 1 in 1,667. By 30, they rise to 1 in 952. At 35, the risk is 1 in 385. At 40, it jumps to 1 in 106, and by 45, it reaches 1 in 30.
Down syndrome is just one form of chromosomal difference. The overall rate of any chromosomal abnormality increases roughly tenfold after age 40 compared to before age 25. In IVF cycles using eggs from women over 42, about 85% of embryos are chromosomally abnormal. This is why prenatal genetic screening becomes especially important for older mothers.
Pregnancy Complications
Two of the most common complications linked to maternal age are gestational diabetes and preeclampsia, a dangerous condition involving high blood pressure. A large study from central China found that women 35 and older had about 76% higher odds of developing gestational diabetes and 74% higher odds of preeclampsia compared to women under 35, even after accounting for other factors like weight.
Ectopic pregnancy, where a fertilized egg implants outside the uterus, also becomes more common. Data from Norway showed that women over 35 had eight times the risk of ectopic pregnancy compared to women aged 15 to 19. This partly reflects the accumulation of risk factors over time, including past pelvic infections and changes to the fallopian tubes.
IVF Success Rates After 40
For women who turn to IVF, maternal age is the single strongest predictor of success. Women over 40 using their own eggs have a live birth rate of only about 3% per cycle. Even after multiple cycles, the cumulative success rate reaches roughly 31% after six attempts, which is still lower than the estimated 44% chance of conceiving naturally within a given timeframe at that age.
This steep drop is driven almost entirely by egg quality rather than uterine health. Using donor eggs from a younger woman dramatically improves success rates, which is why fertility specialists often recommend this option for women in their early to mid-40s.
Prenatal Screening for Older Mothers
Maternal age directly shapes which prenatal tests your provider will recommend. Non-invasive prenatal testing (NIPT), a blood test that screens for chromosomal conditions like Down syndrome using fragments of fetal DNA, is considered medically necessary for women who will be 35 or older at their due date. This test can be done as early as 10 weeks into pregnancy.
For younger women, NIPT may still be available but is not always covered by insurance unless other risk factors are present. Older mothers are also more likely to be offered diagnostic procedures like amniocentesis, which provides a definitive answer about chromosomal conditions rather than a probability estimate.
The Trend Toward Later Motherhood
Despite the medical risks, the average age of motherhood in the United States continues to climb. According to CDC data, the mean age of first-time mothers rose from 26.6 in 2016 to 27.5 in 2023. For all births regardless of birth order, the average was 29.6 in 2023. Similar upward trends appeared for second and third births, continuing a decades-long shift toward delayed childbearing.
This trend reflects broader social changes: more women pursuing higher education, building careers before starting families, and having greater access to contraception. It means that a growing number of pregnancies now fall into the advanced maternal age category, making the term increasingly relevant in routine prenatal care. The medical system has adapted with better screening tools and closer monitoring, but the underlying biological realities of egg aging remain unchanged.