If you’ve been having regular unprotected sex and haven’t gotten pregnant, you’re not alone. About 15% of couples struggle with infertility, and the reasons range from ovulation problems and sperm quality to timing, weight, and structural issues that often have no obvious symptoms. Sometimes multiple smaller factors overlap. Understanding the most common reasons can help you figure out what might apply to you and what to do next.
How Long Is Normal?
Getting pregnant rarely happens on the first try. Even with perfect timing, a healthy couple in their twenties has roughly a 20-30% chance of conceiving in any given cycle. The CDC defines infertility as not conceiving after one year of unprotected sex, and that’s the general benchmark for women under 35. If you’re 35 or older, the threshold drops to six months. Women over 40 should consider seeking evaluation sooner rather than waiting.
These timelines exist because fertility declines steadily with age, particularly after 35. If you’ve only been trying for a few months, the odds may simply need more time to work in your favor. But if you’ve hit those benchmarks, or you already suspect something is off, it’s worth investigating.
Ovulation Problems
The single most common reason women don’t get pregnant is irregular or absent ovulation. Without releasing an egg, conception is impossible. Polycystic ovary syndrome (PCOS) is the leading cause of this worldwide, affecting an estimated 10-13% of women of reproductive age. Up to 70% of women with PCOS don’t know they have it, which means millions of women are trying to conceive without realizing their bodies aren’t ovulating consistently.
Signs that you may not be ovulating regularly include irregular periods (cycles shorter than 21 days or longer than 35), very light or very heavy bleeding, or skipping periods altogether. Some women with PCOS also notice excess facial or body hair, acne, or difficulty losing weight. If your cycles are unpredictable, that’s one of the first things worth discussing with a doctor, because it’s also one of the most treatable causes of infertility.
Sperm Quality Matters Just as Much
Infertility is not just a female issue. A male factor is involved in roughly half of all infertile couples, and in about 20% of cases, it’s the only identified cause. A semen analysis can reveal problems with sperm count, how well sperm swim (motility), and whether sperm are shaped normally (morphology). Any of these can reduce the chances of fertilization, and combinations of all three are common.
Unlike ovulation problems, male factor infertility rarely has visible symptoms. Sperm quality can be affected by heat exposure, certain medications, hormonal imbalances, varicoceles (enlarged veins in the scrotum), smoking, heavy alcohol use, and age. A semen analysis is a straightforward test and should be one of the first steps in any fertility evaluation. It’s far less invasive than most female fertility testing, yet it’s often overlooked or delayed.
Your Fertile Window Is Narrow
Timing plays a bigger role than many people realize. After ovulation, an egg survives only 12 to 24 hours. Sperm, however, can live inside the reproductive tract for three to five days. This means your best odds come from having sex in the three to four days before ovulation and the day of ovulation itself. Having sex after ovulation has likely already passed is far less likely to result in pregnancy.
If you’re not tracking ovulation, you may be missing this window entirely. Ovulation predictor kits, basal body temperature tracking, and cervical mucus changes can all help you identify when you’re most fertile. For most women with a 28-day cycle, ovulation happens around day 14, but this varies widely. Women with longer or shorter cycles often ovulate earlier or later than expected.
Blocked Fallopian Tubes
Even if you’re ovulating normally and sperm quality is fine, the egg and sperm still need to physically meet. Blocked or damaged fallopian tubes prevent this entirely. Endometriosis is one of the most common causes: tissue similar to the uterine lining grows outside the uterus, causing irritation and inflammation. This tissue builds up and breaks down with each menstrual cycle but can’t be shed normally. Over time, it can scar and block the tubes, trap eggs inside the ovaries, or create an environment that prevents fertilization.
Pelvic infections, previous surgeries, and sexually transmitted infections (particularly chlamydia and gonorrhea, which can be asymptomatic) can also cause tubal damage. A blocked tube typically causes no pain or symptoms, which is why it often goes undetected until a fertility workup. Doctors can check for tubal blockages with an imaging test that involves flushing dye through the uterus and tubes.
How Weight Affects Fertility
Body weight has a direct, measurable effect on ovulation. Data from the Nurses’ Health Study shows that as BMI rises above 27, the risk of ovulation-related infertility climbs steadily. Women with a BMI over 30 face roughly 2.7 times the risk compared to women at a normal weight. Between 30% and 36% of women with obesity experience menstrual irregularities, and even among women who do ovulate, higher BMI and more abdominal fat are associated with lower odds of responding to fertility medications.
The effect extends to assisted reproduction as well. Higher BMI correlates with lower implantation rates and lower live birth rates during IVF, in a linear pattern: the higher the weight, the lower the success rate. Being significantly underweight can also disrupt ovulation by suppressing the hormonal signals that trigger egg release. If your weight is well outside the normal range in either direction, addressing it can meaningfully improve your chances.
Unexplained Infertility
Up to 30% of couples who go through a full fertility evaluation receive a diagnosis of “unexplained infertility.” This means the standard tests, which typically include confirming ovulation, checking that at least one fallopian tube is open, and analyzing a semen sample, all come back normal. It’s a frustrating diagnosis, but it doesn’t mean nothing is wrong. It means current testing can’t pinpoint the specific barrier.
Possible hidden factors include subtle egg quality issues, problems with how the embryo implants in the uterine lining, or immune-related responses that aren’t captured by routine bloodwork. Age-related egg quality decline is a major contributor, especially for women in their late 30s and 40s. Despite the uncertainty, couples with unexplained infertility still have treatment options, and many do eventually conceive with approaches that range from timed intercourse with medication to IVF.
Ovarian Reserve Testing
You may have heard about blood tests that measure your egg supply, particularly AMH (anti-Müllerian hormone) and FSH (follicle-stimulating hormone). These tests are commonly used during fertility evaluations, but the results can be misleading if taken out of context. A large study of over 750 women aged 30-44 with no known fertility problems found that women with low AMH or high FSH levels had similar pregnancy rates over 6 and 12 months of trying compared to women with normal levels.
This doesn’t mean these tests are useless. They help fertility specialists predict how your ovaries will respond to stimulation medications during treatments like IVF. But a low AMH on its own does not mean you can’t get pregnant naturally. If you’ve had these tests and received concerning results, the numbers reflect the quantity of eggs remaining, not necessarily their quality or your ability to conceive in a given cycle.
What to Look Into First
If you’ve been trying for the appropriate amount of time based on your age, a basic fertility workup covers three things: confirming that you’re ovulating, checking that your tubes are open, and getting a semen analysis for your partner. These three tests address the majority of identifiable causes. Beyond that, thyroid function and other hormonal screening can catch less obvious issues.
In the meantime, the most actionable steps are tracking your ovulation so you’re timing intercourse correctly, maintaining a healthy weight, limiting alcohol, and cutting out smoking (for both partners). Fertility is rarely about one dramatic problem. More often, it’s a combination of smaller factors that, once identified, can be addressed individually or together.