If you’ve been trying to conceive without success, you’re not alone. About 15% of couples experience infertility, and the reasons range from hormonal imbalances and structural issues to sperm problems and factors that affect both partners simultaneously. Understanding the most common causes can help you figure out what might be going on and whether it’s time to seek help.
How long you should try before worrying depends on your age. Women under 35 are generally advised to try for 12 months before pursuing a medical evaluation. If you’re 35 or older, that window shortens to 6 months. Women over 40 may benefit from earlier evaluation and treatment.
Age Affects Conception More Than Most People Realize
A woman in her early to mid-20s has a 25 to 30% chance of getting pregnant in any given month. That number drops gradually through the 30s and falls sharply after 35. By age 40, the chance of conceiving in a single cycle is around 5%. This decline happens because both the number and quality of eggs decrease over time. Even if your periods are regular, the eggs released each month become less likely to result in a healthy pregnancy as you get older.
This doesn’t mean pregnancy after 35 or 40 is impossible. It means each cycle is less likely to work, so it takes longer on average. If you’re in your late 30s or 40s and have been trying for several months, the math alone could explain the delay.
Ovulation Problems Are the Most Common Female Cause
You can’t get pregnant if you’re not releasing an egg, and irregular or absent ovulation is one of the top reasons women struggle to conceive. Polycystic ovary syndrome (PCOS) is the most common cause of anovulation (not ovulating) worldwide. PCOS is diagnosed when at least two of the following are present: signs of high testosterone like excess facial or body hair, acne, or hair thinning on the scalp; irregular or missing periods; and polycystic-appearing ovaries on ultrasound.
PCOS isn’t the only cause of ovulation problems. Thyroid disorders, high stress levels, very low body weight, and issues with the signals your brain sends to your ovaries can all disrupt the hormonal chain reaction needed to release an egg each month. If your periods are irregular, very light, very heavy, or absent altogether, there’s a good chance ovulation isn’t happening consistently.
Blocked or Damaged Fallopian Tubes
Your fallopian tubes are where sperm meets egg, so any blockage or damage there can prevent conception entirely. Tubal problems account for a significant portion of female infertility, with blockage of the outer end of the tube responsible in about 85% of tubal cases.
The most common cause of tubal damage is pelvic inflammatory disease (PID), typically triggered by sexually transmitted infections like chlamydia or gonorrhea. These infections damage the delicate lining of the tubes, destroying the tiny hair-like cells that help move the egg along. The damage is cumulative: a woman who has had three episodes of PID faces up to a 75% chance of infertility from tubal scarring alone. Other causes include endometriosis, previous abdominal or pelvic surgery, and fibroids near the tube openings. Because many of these conditions cause no obvious symptoms, you may not know your tubes are affected until you’re tested.
Male Fertility Is a Factor in Half of Cases
Fertility conversations often focus on the woman, but male factors play a role in roughly 50% of couples who can’t conceive. In about 20% of infertile couples, a male factor is the only identifiable cause. A semen analysis is one of the first and simplest tests in any fertility workup, and it measures three key things: how many sperm are present (concentration), how well they swim (motility), and how many have a normal shape (morphology).
The minimum healthy benchmarks, set by the World Health Organization, are a concentration of at least 16 million sperm per milliliter, at least 42% of sperm moving, and at least 4% with normal shape. Falling below any of these thresholds reduces the odds of natural conception. Low counts, poor movement, abnormal shape, or a combination of all three are the most frequently identified problems.
Weight plays a role in male fertility too. In men carrying significant excess weight, fat tissue converts testosterone into estrogen at higher rates. This hormonal shift can suppress the signals that drive sperm production, leading to lower testosterone levels and reduced sperm output. For men with a high BMI, weight loss alone can sometimes improve semen quality.
Body Weight and Hormonal Balance
Weight affects fertility on both sides. In women, a BMI above 27 roughly doubles to triples the risk of anovulatory infertility compared to women at a moderate weight. Excess body fat disrupts the balance of reproductive hormones, particularly insulin and estrogen, which can interfere with the regular release of eggs. Being significantly underweight causes problems too, as the body may shut down ovulation to conserve energy.
The good news is that weight-related ovulation problems often respond to relatively modest changes. Losing even 5 to 10% of body weight can restore regular cycles in some women with PCOS or weight-related anovulation.
Environmental Chemicals That Disrupt Hormones
Certain chemicals in everyday products can interfere with reproductive hormones. Known as endocrine disruptors, these substances either mimic hormones or block their normal activity. BPA, found in some plastics and food packaging, has been shown to compromise embryo implantation during a woman’s reproductive years. Lead, even at low levels, can alter reproductive hormones in premenopausal women and may shorten the overall window of fertility.
These chemicals can also affect the precursor cells that eventually become sperm and eggs. While eliminating all exposure is impractical, reducing contact with common sources (plastic food containers, certain pesticides, and contaminated water) is a reasonable step for couples trying to conceive.
Sometimes There’s No Clear Explanation
In 10 to 30% of couples struggling to conceive, every standard test comes back normal. Ovulation is happening on schedule, the fallopian tubes are open, the uterus looks healthy, egg reserves are adequate, and the semen analysis is fine. This is classified as unexplained infertility, and while the label can be frustrating, it doesn’t mean nothing is wrong. It means current testing can’t detect the specific issue.
Possible hidden factors include subtle egg quality problems, issues with how the embryo implants, or sperm function problems that a standard analysis doesn’t capture (like DNA fragmentation within the sperm). Couples with unexplained infertility still have treatment options, and many go on to conceive with interventions that improve the odds each cycle.
Timing and Frequency of Intercourse
Even when everything is working correctly, timing matters. An egg survives only about 12 to 24 hours after ovulation, and sperm can live inside the reproductive tract for up to five days. Your most fertile window is the five days before ovulation and the day of ovulation itself. If you’re only having intercourse outside this window, you could be missing it every month without realizing.
Ovulation typically happens about 14 days before your next period starts, but this varies. Tracking your cycle with ovulation predictor kits, basal body temperature, or cervical mucus changes can help you identify your actual fertile days rather than guessing. Having intercourse every one to two days during your fertile window gives you the best odds each cycle.