Advanced maternal age is generally defined as being 35 or older at the time of delivery. This is the threshold most widely used in clinical practice, though it’s worth knowing that 35 is somewhat arbitrary. The American College of Obstetricians and Gynecologists (ACOG) acknowledges the cutoff is a convention, not a biological cliff, and notes that some risks don’t meaningfully shift until age 40 or later. Beyond 40, the term “very advanced maternal age” applies, and pregnancies at 45 or older are sometimes classified as “extremely advanced maternal age.”
Why 35 Became the Cutoff
The age 35 wasn’t chosen because something dramatic happens to your body on your 35th birthday. It emerged decades ago from genetic counseling, when researchers calculated that at 35 the statistical risk of having a baby with Down syndrome (about 1 in 365) began to approach the risk of complications from amniocentesis, which was then the primary way to screen for chromosomal conditions. That crossover point became a practical line in the sand, and over time it stuck as the default definition of “advanced” maternal age across obstetric guidelines worldwide.
Today, screening technology has evolved considerably, and amniocentesis is no longer the only option. But the 35 threshold persists because it also roughly marks the point at which several pregnancy complications begin to rise in a statistically meaningful way, even in otherwise healthy people with no pre-existing conditions.
What Happens to Egg Supply Over Time
Most girls are born with about 2 million eggs. By adolescence, that number has already dropped to roughly 400,000. By age 37, only about 25,000 remain. The decline isn’t just about quantity. Egg quality, meaning the likelihood that an egg will have the correct number of chromosomes after fertilization, also drops with age. This is why both natural conception rates and fertility treatment success rates decrease as you get older.
IVF outcomes illustrate the shift clearly. In one large institutional study, women under 35 had a cumulative live birth rate of about 70% after up to six IVF cycles. For women over 40, the live birth rate after a first cycle was just 3.1%, and even after four cycles it plateaued around 22%.
Chromosomal Risks by Age
The risk of chromosomal conditions like Down syndrome (trisomy 21) rises steadily with maternal age. At 25, the chance is roughly 1 in 1,300. At 35, it’s about 1 in 365. By 45, the risk jumps to approximately 1 in 30. This increase is driven by the higher likelihood of errors during egg cell division in older eggs, a process that becomes less precise over time.
Modern prenatal screening can detect these conditions early in pregnancy. Cell-free DNA screening, a blood test available in the first trimester, can identify the most common chromosomal abnormalities with high accuracy and carries no physical risk to the pregnancy. ACOG recommends that all pregnant people, regardless of age, be offered both screening and diagnostic testing options.
Pregnancy Complications After 35
Women 35 and older face a higher rate of several pregnancy complications compared to younger women, even when they’re healthy going in. A large study in central China found that women 35 or older had about 74% higher odds of developing preeclampsia (a dangerous rise in blood pressure during pregnancy) and 76% higher odds of gestational diabetes compared to women under 35. In raw numbers, gestational diabetes affected 22.5% of women 35 and older versus 14% of younger women. Preeclampsia rates were 3.6% versus 1.9%.
These aren’t rare conditions at any age, but the gap widens enough to change how your care team monitors your pregnancy. You can expect more frequent blood pressure checks, earlier and more thorough glucose screening, and potentially more ultrasounds in the third trimester to monitor fetal growth.
What Happens After 45
Pregnancies at 45 and beyond carry a distinct risk profile. In a review of 79 deliveries to women aged 45 to 47 and older across four hospitals, nearly half (46.8%) experienced obstetric complications during pregnancy. Gestational diabetes occurred in about 13% and preeclampsia in about 10%. Roughly 1 in 10 pregnancies had a diagnosed chromosomal abnormality. The cesarean delivery rate was 31.7%, often due to abnormal fetal positioning or fetal distress during labor.
That said, the same study found that maternal and fetal outcomes were “generally good” overall. Median birth weight was normal, and many of these pregnancies ended without major incident. The takeaway isn’t that pregnancy after 45 is impossible or inevitably dangerous, but that close monitoring becomes especially important because complications are common enough to require active management.
Labor and Delivery Differences
Cesarean delivery rates are consistently higher in pregnancies over 35, and they climb further after 40. Several factors contribute: older uterine muscle may contract less efficiently during labor, the baby is more likely to be in an unusual position, and care teams tend to have a lower threshold for surgical delivery when monitoring shows any signs of fetal distress. The risk of preterm birth also rises modestly, as does the likelihood of having either a very small or very large baby.
About 15% of infants born to mothers over 45 required time in the neonatal intensive care unit in the hospital-based study mentioned above, and roughly 17% were born at a low birth weight. These numbers reflect the cumulative effect of age-related changes rather than any single complication.
Paternal Age Matters Too
The conversation around parental age usually focuses on the mother, but paternal age also affects birth outcomes. Data from over 40 million births in the United States, published by researchers at Stanford Medicine, showed that babies born to fathers 45 or older were 14% more likely to be born prematurely, 14% more likely to have a low birth weight, and 18% more likely to experience seizures at birth compared to babies born to fathers aged 25 to 34. Advanced paternal age is loosely defined as 35 and older, though the most significant risks appear after 45.
Putting the Numbers in Context
Birth rates among women over 35 have been climbing for three decades. More people are choosing to build careers, establish financial stability, or wait for the right circumstances before starting a family. Advances in fertility treatments have also extended the reproductive window in ways that weren’t possible a generation ago.
Being 35 or older doesn’t mean your pregnancy is destined for complications. Most people in this age group have healthy pregnancies and healthy babies. What the “advanced maternal age” label really signals is that your pregnancy warrants a bit more attention: earlier screening, more frequent monitoring, and open conversations with your care team about what your individual risk factors look like. Age is one variable among many, including weight, blood pressure, family history, and overall health, that shape how your pregnancy will go.