About one in six people of reproductive age experience infertility at some point, so if you’ve been trying without success, you’re far from alone. The causes range from hormonal imbalances and structural problems to sperm issues and simple timing. In many cases, the reason is identifiable and treatable.
How Long Is Normal?
If you’re under 35 and have been having regular unprotected sex for less than a year, it may simply be too early to worry. Healthy couples with no fertility issues still only have about a 20 to 30 percent chance of conceiving in any given cycle, which means several months of trying is completely normal.
The general guideline is to seek a medical evaluation after 12 months of trying without success. If you’re 35 or older, that timeline shortens to six months. These aren’t arbitrary cutoffs. They reflect the statistical reality that most fertile couples will conceive within that window, and earlier investigation gives you more options if something needs to be addressed.
You May Not Be Ovulating Regularly
The single most common reason women struggle to conceive is irregular or absent ovulation. Without releasing an egg each cycle, pregnancy simply can’t happen. Polycystic ovary syndrome (PCOS) is the leading cause of chronic ovulation problems in premenopausal women, but it’s not the only one.
Thyroid disorders, both overactive and underactive, can disrupt ovulation. So can excessive exercise, significant weight loss, high stress levels, obesity, diabetes, depression, and certain medications including some antidepressants. A condition called functional hypothalamic amenorrhea occurs when the brain essentially dials down the reproductive signals that trigger egg release, often in response to low body weight, intense physical training, or chronic stress.
Clues that you may not be ovulating include very irregular periods (cycles shorter than 21 days or longer than 35), absent periods, or cycles where you never notice changes in cervical mucus. But some women with seemingly regular periods still don’t ovulate every cycle, which makes tracking more complicated.
It Could Be a Sperm Issue
Male factors contribute to roughly half of all infertility cases, yet they’re often the last thing couples investigate. A semen analysis is one of the simplest and most informative early tests. The World Health Organization considers a normal sample to have a sperm concentration of at least 16 million per milliliter, total motility (the percentage of sperm that are moving) of 42% or higher, and progressive motility of at least 30%.
Low sperm count, poor motility, and abnormal sperm shape can all reduce the odds of fertilization. Common contributors include varicoceles (enlarged veins in the scrotum), hormonal imbalances, heat exposure, certain medications, smoking, heavy alcohol use, and obesity. In men carrying excess body fat, testosterone can be converted to estrogen in fat tissue, which suppresses the hormonal signals that drive sperm production.
Structural Problems That Block Fertilization
Even when ovulation and sperm are both normal, physical barriers can prevent egg and sperm from meeting. Blocked or damaged fallopian tubes are a common culprit, often resulting from past pelvic infections, prior surgeries, or endometriosis.
Endometriosis deserves special attention because it affects fertility through multiple pathways at once. The inflammatory environment it creates in the pelvis can damage sperm, reduce sperm mobility, and interfere with the interaction between sperm and egg. It can also disrupt ovulation directly: women with endometriosis tend to have higher prolactin levels, which interfere with the hormonal pulses needed to trigger egg release. In some cases, a follicle will go through all the hormonal motions of ovulation but never actually rupture to release the egg.
Endometriosis can also compromise the uterine lining itself. Endometriotic tissue outside the uterus competes for stem cells that the uterus needs for proper repair and regeneration each cycle, potentially making it harder for an embryo to implant even when fertilization does occur.
Uterine fibroids, polyps, and scar tissue inside the uterus can also interfere with implantation, depending on their size and location.
Age and Egg Supply
Age is the single strongest predictor of fertility, and its effects are more dramatic than most people realize. Women are born with about 2 million eggs. By puberty, that number has already dropped to roughly 400,000. By age 37, only about 25,000 remain. The decline isn’t just in quantity. Egg quality, meaning the likelihood that an egg will produce a chromosomally normal embryo, drops significantly after the mid-30s and accelerates after 40.
This doesn’t mean pregnancy after 35 is impossible, but it does mean each cycle carries lower odds, and the risk of miscarriage rises. If you’re in your late 30s or 40s and have been trying for several months, the timeline for seeking help is shorter for good reason.
How Body Weight Affects Fertility
Both ends of the weight spectrum can interfere with conception. In women with obesity, excess fat tissue converts androgens into estrogen, which disrupts the hormonal feedback loop between the brain and the ovaries. This can cause irregular cycles, reduced egg quality, and impaired function of the cells that support egg development. The effects extend to insulin regulation as well, which is closely tied to ovulation.
Being significantly underweight causes a different problem. The brain may interpret low energy availability as a signal that the body can’t support a pregnancy, and it reduces the hormonal output needed for ovulation. This is the mechanism behind exercise-related and stress-related missed periods.
There’s no single BMI number that marks a hard line between fertile and infertile, but moving toward a moderate weight range can meaningfully improve ovulation regularity for many women.
Tracking Ovulation Correctly
One surprisingly common reason for not conceiving is mistiming intercourse. You’re most fertile in the one to two days before ovulation, not after it. This makes the method you use to predict ovulation important.
Basal body temperature tracking, where you take your temperature every morning before getting out of bed, confirms that ovulation happened but only after the fact. By the time your temperature spikes, the egg has already been released and is no longer viable. This method is useful for understanding your cycle patterns over several months but won’t help you time things in real time.
Ovulation prediction kits (OPKs), which detect the hormone surge that triggers ovulation, are more useful for timing because they signal that ovulation is about to happen. The main downsides are that you can miss the surge if you skip a day of testing or if your urine is too dilute, and the kits add up in cost over multiple months. For the best odds, having sex every one to two days during the week surrounding your expected ovulation is more reliable than trying to pinpoint a single day.
What Testing Looks Like
When you do see a specialist, the initial workup is straightforward. For women, it typically includes blood tests to measure key hormones. FSH, tested on day two or three of your cycle, helps assess egg quality. AMH, which can be drawn at any point in your cycle, reflects the quantity of eggs remaining in your ovaries, though it doesn’t predict your chance of conceiving in any specific month. A transvaginal ultrasound counts the small follicles visible on your ovaries, providing another measure of ovarian reserve.
An imaging test to check whether the fallopian tubes are open is also standard. For men, a semen analysis is usually the first and most important step. Together, these tests identify a cause in the majority of cases.
When No Cause Is Found
Up to 30% of couples who undergo a full evaluation receive a diagnosis of unexplained infertility. This doesn’t mean nothing is wrong. It means the standard tests didn’t catch it. Subtle issues with egg quality, sperm function at the molecular level, or embryo implantation can all escape detection with current tools.
The typical treatment path for unexplained infertility starts with three or four cycles of ovarian stimulation using oral medication combined with intrauterine insemination. This approach works by increasing the number of eggs released per cycle and placing sperm closer to where fertilization happens. For couples who don’t conceive after those initial cycles, IVF is the recommended next step and carries substantially higher success rates per cycle.