If you’ve been having regular, unprotected sex and haven’t gotten pregnant, you’re facing one of the most common and frustrating experiences in reproductive health. About one in eight couples struggles to conceive. The causes split roughly evenly between female factors, male factors, and a combination of both, so this is rarely a one-person problem. Understanding the most likely reasons can help you figure out what to investigate first.
The general medical guideline is to seek evaluation after 12 months of trying if you’re under 35, or after 6 months if you’re 35 or older. But even before that point, knowing what can interfere with conception gives you a head start.
You May Be Missing Your Fertile Window
One of the simplest explanations is timing. You can only get pregnant during a narrow stretch of your cycle: the five days before ovulation, the day of ovulation itself, and the day after. Outside that window, conception isn’t possible regardless of how frequently you have sex. For someone with a textbook 28-day cycle, ovulation typically falls around day 14, but many people don’t have textbook cycles. Stress, travel, illness, and hormonal shifts can move ovulation earlier or later without warning.
Tracking ovulation with at-home test strips, basal body temperature, or cervical mucus changes can help you identify your actual fertile window rather than guessing. Having sex every day or every other day during that window gives you the best odds. Even with perfect timing, though, a woman in her early to mid-20s only has a 25 to 30% chance of conceiving in any given month. That number is lower than most people expect, and it means several months of well-timed attempts with no pregnancy is completely normal.
Ovulation Problems Are the Most Common Female Factor
If your body isn’t releasing an egg regularly, conception can’t happen. Irregular or absent ovulation is the single most common reason women have difficulty getting pregnant, and it shows up as irregular periods, very long cycles, or skipped periods entirely.
Polycystic ovary syndrome (PCOS) is the leading cause of ovulation problems. It creates a hormone imbalance that can prevent your ovaries from releasing a mature egg each month. PCOS affects up to 10% of women of reproductive age and often comes with other signs like acne, excess hair growth, or difficulty managing weight. It’s highly treatable once diagnosed.
Stress and body weight also directly affect ovulation. Your brain produces two key hormones that trigger egg release each cycle. Excess physical or emotional stress, very high or very low body weight, or a recent significant change in weight can disrupt production of those hormones and shut down ovulation. A BMI below 18.5 often causes irregular cycles and may stop ovulation altogether. A BMI in the obese range (above 30) can do the same. Even moving from a normal weight into the overweight category can shift your cycles. The encouraging part is that ovulation often resumes once the underlying trigger is addressed.
Structural Issues Can Block Egg and Sperm From Meeting
Even when ovulation is happening on schedule, physical barriers in the reproductive tract can prevent pregnancy. The fallopian tubes are where egg and sperm actually meet, and they’re extremely fragile. If they’re blocked or scarred, there’s no way for fertilization to occur.
Endometriosis is one of the most common causes. Tissue similar to the uterine lining grows in places it shouldn’t, including on the ovaries, fallopian tubes, and pelvic cavity lining. This tissue builds up and breaks down with each menstrual cycle but can’t be shed the way normal tissue is during a period. The result is chronic irritation, inflammation, and scarring that can trap eggs inside the ovaries, block the tubes, or prevent a fertilized egg from implanting in the uterus. Endometriosis affects roughly 1 in 10 women and sometimes causes painful periods or pelvic pain, but it can also be completely silent.
Pelvic inflammatory disease, usually caused by untreated sexually transmitted infections, can also damage the tubes. Some women have structural differences in the uterus itself, like fibroids or polyps, that interfere with implantation.
Male Factors Account for Nearly Half of Cases
This is the piece many couples overlook. Problems with sperm count, movement, or shape contribute to infertility in roughly 40 to 50% of couples who can’t conceive. A semen analysis is one of the first and easiest tests to run, yet it’s often delayed because couples assume the issue is on the female side.
The most common treatable cause of male infertility is a varicocele, which is a swelling of the veins that drain the testicle. It raises the temperature around the testicles and can lower both sperm count and quality. Surgery to correct it often improves sperm numbers and movement. Genetic conditions, prior surgeries, and certain medications for depression, high blood pressure, arthritis, or digestive problems can also reduce sperm production significantly.
Lifestyle plays a measurable role too. Smoking causes a significant drop in sperm count and quality. One large study found that smokers had total sperm counts roughly 17.7 million lower than nonsmokers. Smoking also damages sperm DNA through oxidative stress, which can affect fertilization and early embryo development even when counts look adequate. Excess body fat around the scrotum raises testicular temperature and creates the same kind of oxidative damage. Heavy alcohol use, anabolic steroids, and prolonged heat exposure from hot tubs or laptops on the lap can compound the problem.
Age Affects Fertility More Than Most People Realize
Female fertility declines gradually starting in the late 20s, more noticeably after 35, and steeply after 40. A woman in her early 20s has about a 25 to 30% chance of conceiving in any given cycle. By 40, that chance drops to around 5% per cycle. This decline reflects both a shrinking number of eggs and a higher rate of chromosomal abnormalities in the remaining eggs, which leads to more failed implantations and early miscarriages.
Male fertility also declines with age, though more gradually. Sperm quality, including DNA integrity and motility, decreases over time. Couples where both partners are over 35 face compounding effects that make each month of trying less likely to succeed, which is why the medical recommendation shifts to seeking evaluation after just 6 months rather than 12.
What Testing Looks Like
A fertility evaluation typically involves both partners from the start. For the male partner, it begins with a semen analysis, which measures sperm count, movement, and shape. The sample is collected after 48 to 72 hours of abstinence from ejaculation. This single test can rule in or rule out a major category of problems quickly and inexpensively.
For the female partner, the initial workup usually includes a blood test to confirm ovulation is occurring. This is done by measuring progesterone levels about a week before your expected period. If there’s concern about egg supply, your doctor may check ovarian reserve through a blood test that measures a hormone reflecting how many eggs remain. An imaging test called a hysterosalpingogram uses dye to check whether the fallopian tubes are open and whether the uterus has a normal shape. It’s typically recommended for women without a known history of pelvic infection or endometriosis.
These first-line tests identify a cause in the majority of cases. When they don’t, further investigation might include more detailed imaging, hormonal panels, or genetic testing.
What You Can Do Right Now
While you’re figuring out the bigger picture, a few changes can meaningfully improve your odds. If your BMI is outside the 19 to 24 range, moving toward that window can restore regular ovulation and improve sperm quality. If either partner smokes, quitting removes a direct source of reproductive damage. Reducing alcohol to moderate levels, managing chronic stress, and ensuring adequate sleep all support hormonal balance for both partners.
Start taking 400 micrograms of folic acid daily if you aren’t already. While folic acid doesn’t increase your chances of conceiving, it’s critical for early brain and spinal cord development in the embryo, and those structures form before most people even know they’re pregnant. The CDC recommends all women capable of becoming pregnant take it every day.
If you’ve been tracking ovulation and timing intercourse well for several months without success, getting both partners tested sooner rather than later removes the guesswork. Many causes of delayed conception are straightforward to identify and treat once someone actually looks.