A woman can technically get pregnant from the time she starts ovulating, which happens around her first period near age 12, until she reaches menopause at an average age of 52. That’s a roughly 40-year window, but fertility is far from equal across it. The chances of conceiving naturally peak in the early 20s and decline significantly after 35, with both egg quantity and egg quality dropping steadily over time.
When Fertility Begins
Pregnancy becomes possible once a girl begins ovulating, which typically starts shortly after her first menstrual period. In the United States, the median age of first menstruation is about 11 years and 10 months. By age 10, roughly 10% of girls have already started their periods. By age 14, about 90% have. Ovulation doesn’t always happen consistently in those early cycles, but pregnancy is biologically possible from this point forward.
Peak Fertility: Your 20s
Fertility is highest in the early to mid-20s. A woman between 20 and 24 who is actively trying to conceive has about an 86% chance of getting pregnant within one year. Between ages 25 and 29, that number dips slightly to around 78%. These are the years when egg quality is at its best, miscarriage risk is low, and pregnancy complications are least common.
Girls are born with about 2 million eggs. By the time they reach puberty, that number has already dropped to roughly 400,000. The body doesn’t make new eggs; it draws from this existing supply for the rest of reproductive life.
The Shift After 30
Fertility begins a noticeable decline in the early 30s. Between ages 30 and 34, the chance of conceiving within a year of trying drops to about 63%. Between 35 and 39, it falls further to around 52%. By age 37, only about 25,000 eggs remain, and the eggs that are left are more likely to have chromosomal abnormalities.
This is why 35 is the age that comes up so often in conversations about pregnancy timing. The American College of Obstetricians and Gynecologists uses 35 as the threshold for what’s sometimes called “advanced maternal age,” not because fertility ends at 35, but because the statistical risks of complications begin rising more steeply from this point.
Miscarriage risk follows a similar curve. It’s lowest for women aged 25 to 29, at about 10%. After 30 it rises steadily, and by age 45 and older, more than half of pregnancies end in miscarriage.
Pregnancy Risks After 35
Women over 35 face higher rates of several pregnancy complications: gestational diabetes, preeclampsia (dangerously high blood pressure during pregnancy), preterm birth, low birth weight, and the need for a cesarean delivery. The risk of having a baby with a chromosomal condition like Down syndrome also increases because older eggs are more prone to errors during cell division.
These risks are still relatively small for any individual pregnancy, but they’re large enough that doctors typically recommend more frequent monitoring. That might mean earlier screening for gestational diabetes, additional ultrasounds, or closer blood pressure tracking throughout pregnancy.
Fertility in Your 40s
Getting pregnant naturally in your 40s is harder but far from impossible. Women aged 40 to 44 have roughly a 30% chance of conceiving naturally per year. Between 45 and 49, that drops to about 10% per year. After 50, spontaneous pregnancy is rare but has been documented.
Even with IVF using a woman’s own eggs, success rates drop sharply in the mid-40s. Studies of IVF cycles in women 40 to 49 show live birth rates falling to around 6% at age 45 and essentially reaching zero by 48 or 49. IVF with donor eggs from a younger woman has much higher success rates, but using your own eggs at these ages is a long shot.
Perimenopause: Still Fertile
Perimenopause is the transitional phase before menopause, and it can last several years. Periods may become irregular, cycles may be longer or shorter, and ovulation becomes unpredictable. But unpredictable doesn’t mean absent. Up to five years before menopause, nearly 88% of menstrual cycles still show signs of ovulation. Even within the final year before a woman’s last period, about 23% of cycles still involve ovulation.
This is why unintended pregnancies during perimenopause happen more often than people expect. If you don’t want to become pregnant, birth control is recommended until you’ve gone a full 12 months without any period or spotting. Only after that year-long gap is menopause confirmed.
When Pregnancy Is No Longer Possible
Menopause marks the definitive end of natural fertility. The average age in the United States is 52, but it can happen anywhere from the early 40s to the late 50s. The oldest confirmed natural conception on record was a woman in the UK who gave birth at age 59 after conceiving spontaneously past what she thought was her final period.
That case is an extreme outlier. For most women, the practical window for natural conception closes in the mid-40s, even though the biological window technically stays open until menopause is complete. The combination of very few remaining eggs, lower egg quality, and high miscarriage rates means that pregnancies after 45 are uncommon, and healthy pregnancies carried to term are rarer still.