Advanced maternal age is the clinical term for pregnancy at age 35 or older, measured at the expected delivery date. The threshold was originally chosen because of a noticeable increase in chromosomal abnormalities and declining fertility around this age, though the American College of Obstetricians and Gynecologists has acknowledged it’s an arbitrary cutoff. Many risks associated with older age don’t meaningfully shift outcomes until 40 or later.
Why 35 Became the Cutoff
The age of 35 wasn’t chosen because something dramatic happens on that birthday. It was selected decades ago because population data showed fertility declining and genetic risks rising in a way that became harder to ignore around the mid-thirties. The designation stuck, and it’s been used in medical literature ever since. In practice, risk increases gradually, not in a sudden jump. A 34-year-old and a 36-year-old face very similar odds for most outcomes.
How Fertility Changes With Age
Women are born with all the eggs they’ll ever have, and both the number and quality of those eggs decline over time. The drop in egg reserves accelerates noticeably around age 38 to 39. At the cellular level, older eggs are more likely to have errors during cell division, partly due to accumulated oxidative stress and reduced energy production within the egg itself. The outer shell of the egg also hardens with age, which can make fertilization more difficult.
These biological changes translate directly into lower chances of conceiving each month. A large North American study tracking couples trying to get pregnant found that women aged 37 to 39 were about 40% less likely to conceive in any given cycle compared to women aged 21 to 24. For women aged 40 to 45, that gap widened to 60% less likely per cycle. After 12 months of trying, roughly 71% of women in their early twenties had conceived, compared to about 67% of women aged 37 to 39 and 56% of women aged 40 to 45. The decline is real but not a cliff: most women in their late thirties who are trying to conceive will still get pregnant within a year.
For those who turn to fertility treatments like IVF, success rates also drop with age. Live birth rates per IVF cycle for women 40 and older fall to around 3%, with most successful outcomes concentrated in women under 42. Using donor eggs from younger women can substantially improve those odds, which is why it’s commonly offered to women in their early forties.
Miscarriage Risk by Age
The rising rate of chromosomal errors in eggs is the main reason miscarriage becomes more common with age. Between ages 20 and 30, the chance of miscarriage is roughly 9% to 17%. At 35, it rises to about 20%, or one in five pregnancies. By 40, the risk reaches approximately 40%. This increase is driven largely by eggs with the wrong number of chromosomes, which often result in pregnancies that aren’t viable.
Chromosomal Abnormalities
Down syndrome (trisomy 21) is the chromosomal condition most closely tracked by maternal age, but it’s not the only one. The risk of trisomy 13 and trisomy 18 also rises. At age 35, trisomy 21 occurs in roughly 3 out of every 1,000 fetuses. By 40, that rate jumps to about 15 per 1,000, and by 45 it reaches approximately 45 per 1,000. When all three common chromosomal trisomies are counted together, the combined rate goes from about 5 per 1,000 at age 35 to roughly 62 per 1,000 at age 45.
Prenatal screening has advanced significantly. First-trimester blood tests combined with ultrasound can estimate chromosomal risk early in pregnancy. Cell-free DNA testing, which analyzes fragments of fetal DNA circulating in the mother’s blood, is even more accurate and can be done as early as 10 weeks. These screens help identify pregnancies that might benefit from diagnostic testing like amniocentesis, which gives a definitive answer.
Pregnancy Complications
Women 35 and older face a higher risk of two major pregnancy complications: preeclampsia (dangerously high blood pressure) and gestational diabetes. In one large study, preeclampsia occurred in 3.6% of women 35 and older, compared to 1.9% of younger women. Gestational diabetes appeared in 22.5% of the older group versus 14% of younger women. After adjusting for other health factors, being 35 or older roughly doubled the odds of either condition, with adjusted odds around 1.7 times higher for both.
Body weight amplifies these risks significantly. Women who entered pregnancy both overweight and over 35 had nearly six times the odds of preeclampsia and close to three times the odds of gestational diabetes compared to normal-weight women under 35. This means that maintaining a healthy weight before pregnancy is one of the most impactful things women of advanced maternal age can do to lower their risk.
Stillbirth Risk
A systematic review of 37 studies found that maternal age consistently increased the risk of stillbirth, with relative risks ranging from 1.2 to 4.5 times higher for older compared to younger women. The most carefully adjusted studies placed the risk at 1.3 to 1.9 times higher for women over 35. That sounds alarming in relative terms, but the absolute risk remains low: in most industrialized countries, the stillbirth rate among older women is less than 10 per 1,000 births. The vast majority of pregnancies in women over 35 result in a live birth with appropriate care.
Because of this elevated risk, many providers discuss the timing of delivery. Induction of labor at 39 weeks is sometimes offered to women of advanced maternal age to reduce the small but real risk of late stillbirth, though this is a shared decision between you and your provider based on your specific situation.
What Prenatal Care Looks Like
Pregnancies at 35 and older are monitored more closely, but the experience isn’t dramatically different from standard prenatal care. You can generally expect a first-trimester ultrasound, early screening for chromosomal conditions, and potentially earlier glucose testing for gestational diabetes. Some women are started on low-dose aspirin to reduce preeclampsia risk. Later in pregnancy, additional fetal monitoring (like non-stress tests or extra ultrasounds) may be recommended to check on the baby’s wellbeing, particularly as the due date approaches.
None of these additional steps mean your pregnancy is automatically high-risk. They’re precautionary measures that reflect slightly elevated statistical odds, not certainties. Most women over 35 have healthy, uncomplicated pregnancies and deliveries. The label “advanced maternal age” is a screening category, not a diagnosis.