About 13.4% of women ages 15 to 49 in the United States have what’s called impaired fecundity, meaning difficulty getting pregnant or carrying a pregnancy to term. That number holds whether a woman has had children before (13.1%) or never has (13.8%). Infertility affects up to 15% of couples overall, but the chances vary significantly depending on age, underlying health conditions, and lifestyle factors.
How Infertility Is Defined
Infertility isn’t diagnosed after a single month of trying. For women under 35, the clinical threshold is 12 months of regular, unprotected sex without conception. For women over 35, that window shortens to 6 months, reflecting the faster pace of age-related fertility decline. Meeting this definition doesn’t mean pregnancy is impossible. It means the odds are low enough that medical evaluation is warranted.
How Age Changes the Odds
Age is the single biggest factor in female fertility, and the decline is steeper than most people expect. Women 30 and younger have roughly a 20% chance of conceiving in any given menstrual cycle. By age 40, that drops to about 5% per cycle. After 45, both conceiving and carrying a pregnancy to term become rare.
The reason is straightforward: women are born with all the eggs they’ll ever have, and both the number and quality decline over time. At age 30, a healthy woman typically has around 14 follicles visible on ultrasound (a proxy for remaining egg supply). By 40, that median count drops to about 6. Fewer eggs means fewer chances each cycle, and the eggs that remain are more likely to have chromosomal issues that prevent a viable pregnancy or lead to miscarriage.
Common Causes of Female Infertility
When a woman does struggle with fertility, the cause usually falls into a few categories: ovulation problems, structural issues with the fallopian tubes or uterus, endometriosis, or unexplained factors.
Ovulation disorders are the most common culprit. Polycystic ovary syndrome (PCOS) is the leading one, causing hormonal imbalances that prevent eggs from being released on a regular schedule. Globally, PCOS accounts for a larger share of infertility than endometriosis does. Other ovulation disruptors include excess physical or emotional stress, very high or very low body weight, and pituitary gland problems that throw off the hormones responsible for triggering egg release each month.
Endometriosis, where tissue similar to the uterine lining grows outside the uterus, also contributes to infertility, though its overall burden is lower than PCOS, partly because surgical and assisted reproductive treatments for endometriosis-related infertility tend to be effective. Tubal disease, where the fallopian tubes are blocked or damaged (often from past infections), is another well-established cause.
A significant portion of infertility cases have no identifiable cause. Unexplained infertility actually represents the largest category globally when measured by prevalence rates. This can be frustrating, but it also means that many of these cases respond to fertility treatments even without a clear diagnosis.
Signs That May Point to a Problem
The most telling signal is your menstrual cycle. Cycles shorter than 21 days, longer than 35 days, or highly irregular can indicate that ovulation isn’t happening consistently. Absent periods are an even clearer red flag. These patterns don’t guarantee infertility, but they correlate strongly with ovulatory dysfunction.
Other signs are subtler and often overlap with conditions people live with for years before trying to conceive: very painful periods (common with endometriosis), significant acne or excess hair growth (common with PCOS), or unexplained weight changes. None of these confirm infertility on their own, but they’re worth mentioning to a doctor, especially if you’ve been trying to conceive without success.
Lifestyle Factors That Lower Fertility
Several modifiable habits have a measurable impact on your chances of conceiving. Smoking more than 10 cigarettes a day decreases fertility. Drinking more than 4 alcoholic beverages per week is associated with reduced fertility as well. Even caffeine plays a role: consuming more than about 250 milligrams daily (roughly two cups of coffee) is linked to a modest but statistically significant decline in fertility.
Body weight matters on both ends of the spectrum. A BMI above 27 or below 17 is associated with increased rates of anovulatory infertility, meaning the body stops releasing eggs regularly. This is one of the more actionable risk factors, since reaching a healthier weight range can restore ovulation in many cases.
Secondary Infertility Is More Common Than You’d Think
Having had a child before doesn’t protect you from fertility problems the next time around. Secondary infertility, the inability to conceive or carry a pregnancy after previously having a baby, is actually quite common. Global estimates vary widely by region, but studies have placed secondary infertility rates between 7% and 33% of women, depending on the population studied. In some analyses, secondary infertility is more prevalent than primary infertility. Age is often the driving factor: a woman who conceived easily at 28 may face a very different reality at 36.
What IVF Success Looks Like by Age
For women who pursue in vitro fertilization, success rates follow the same age gradient. Based on 2022 national data from fertility clinics, live birth rates per embryo transfer break down like this for fresh embryo transfers:
- Under 35: about 44% live birth rate per transfer
- 35 to 37: about 37%
- 38 to 40: about 24%
- 41 to 42: about 15%
- Over 42: about 5%
When embryos are genetically screened before transfer (a process that selects chromosomally normal embryos), the numbers improve dramatically and stay more stable across age groups. Women under 35 see about a 55% live birth rate per transfer, while women over 42 still achieve around 46%. The catch is that older women produce fewer viable embryos to screen in the first place, so the per-transfer rate can be misleading. It may take more cycles of egg retrieval to get a usable embryo.
These numbers reflect averages across hundreds of clinics. Individual outcomes depend on the specific cause of infertility, overall health, and the clinic’s protocols. But the broad pattern is consistent: fertility treatment can meaningfully improve the odds, especially when started earlier rather than later.