Even with perfectly timed sex, the odds of conceiving in any single month top out at about 25 to 30 percent for women in their early to mid-twenties. That number drops steadily with age, falling to roughly 5 percent per cycle by age 40. So the first thing to understand is that not getting pregnant right away is statistically normal, not a sign that something is wrong. But when months keep passing without a positive test, there are several concrete reasons worth exploring.
How Long Is Normal?
The American Society for Reproductive Medicine recommends that women under 35 try for 12 months of regular, unprotected sex before seeking a fertility evaluation. For women 35 and older, that timeline shortens to 6 months. If you’re over 40, a more immediate evaluation is reasonable. And if you already know about a medical condition linked to fertility, such as irregular periods, endometriosis, or a history of pelvic infections, there’s no reason to wait at all.
These timelines exist because conception is a numbers game even when everything is working. Most healthy couples under 35 will conceive within a year. The fact that it takes several cycles doesn’t point to a problem. It reflects how narrow the biological window actually is each month.
You May Be Missing the Fertile Window
Your body is only capable of conceiving during about six days per cycle: the five days before ovulation and the day of ovulation itself. Sperm can survive in the reproductive tract for up to five days, but an egg only lives about 12 to 24 hours after release. If sex doesn’t happen within that window, pregnancy isn’t possible that month regardless of how healthy you are.
The best approach, according to the American College of Obstetricians and Gynecologists, is to have sex every day or every other day during this six-day window. Cervical mucus, which becomes clear and slippery, typically peaks one to two days before ovulation and serves as a practical signal. Ovulation predictor kits that detect a hormone surge in your urine can also help narrow the timing. If your cycles are irregular, pinpointing this window becomes harder, which is itself worth investigating.
Ovulation Problems Are the Most Common Female Factor
If your body isn’t releasing an egg regularly, conception can’t happen. The most frequent cause of ovulation problems is polycystic ovary syndrome (PCOS), which affects how the ovaries develop and release eggs. In PCOS, the ovaries produce excess androgens (sometimes called “male hormones,” though all women make them in small amounts). This excess triggers the recruitment of many small follicles that never fully mature. Without a dominant follicle, no egg is released.
The hormonal imbalance in PCOS doesn’t stop at the ovaries. Elevated androgens can also reduce progesterone production and make the uterine lining less receptive to a fertilized egg. The lining may thicken unevenly under prolonged estrogen exposure without the normal shedding that comes with regular cycles. Inflammation and disrupted insulin signaling in the uterus compound these effects further. The hallmark signs of PCOS include irregular or absent periods, acne, and excess hair growth, but some women have the condition without obvious symptoms.
Other causes of irregular ovulation include thyroid disorders, being significantly underweight or overweight, high stress levels, and excessive exercise. A blood test measuring your hormone levels on specific days of your cycle can confirm whether you’re ovulating.
Your Partner’s Sperm Matters Just as Much
Male factor infertility is involved in roughly half of all couples who struggle to conceive, and in about 20 percent of cases, it’s the sole cause. A semen analysis is one of the first and simplest tests in a fertility workup, yet it’s often overlooked or delayed because couples assume the issue lies with the woman.
The World Health Organization considers sperm concentration normal at 16 million or more per milliliter, with at least 42 percent of sperm showing movement and at least 4 percent having normal shape. Falling below any of these thresholds reduces the chances that a sperm will successfully reach and fertilize an egg. Problems can include low sperm count, poor motility (sperm that don’t swim well), abnormal shape, or combinations of all three.
Many causes of low sperm quality are treatable or modifiable. Varicoceles (enlarged veins in the scrotum), hormonal imbalances, certain medications, excessive heat exposure, smoking, and heavy alcohol use can all affect sperm production. A semen analysis is painless and provides results quickly, making it one of the most efficient steps in figuring out why pregnancy hasn’t happened.
Blocked or Damaged Fallopian Tubes
The fallopian tubes are where fertilization actually occurs. If one or both tubes are blocked or scarred, the egg and sperm can’t meet. This accounts for a significant share of female infertility and can exist without any noticeable symptoms.
Common causes of tubal damage include past pelvic infections (particularly from chlamydia or gonorrhea), pelvic inflammatory disease, endometriosis, previous abdominal surgery, and even a ruptured appendix. Many women don’t realize they had an infection that caused scarring, especially since chlamydia is often silent.
Doctors typically check for tubal blockages using a test called an HSG, where a liquid is passed through the uterus and tubes while an X-ray tracks whether it flows freely. If the liquid passes through, the tubes are open. It’s worth knowing that this test has a false-positive rate of about 15 percent, meaning it sometimes suggests a blockage that isn’t really there. If results are unclear, a minimally invasive procedure called laparoscopy can provide a direct look at the tubes and surrounding tissue.
Age and Egg Supply
Age is the single strongest predictor of fertility, and its effect is steeper than most people expect. The monthly chance of conception drops from 25 to 30 percent in the early twenties to around 5 percent by 40. This decline reflects two things: fewer eggs remaining in the ovaries and a higher percentage of those eggs carrying chromosomal abnormalities, which lead to failed implantation or early miscarriage.
A blood test measuring anti-Müllerian hormone (AMH) gives a snapshot of your remaining egg supply. Average levels fall between 1.0 and 3.0 ng/mL. Levels below 1.0 are considered low, and levels around 0.4 or below are severely low. AMH doesn’t measure egg quality, but a low result combined with age can help explain why conception is taking longer and guide decisions about treatment urgency.
Weight and Lifestyle Factors
Body weight has a direct, measurable effect on fertility. A high BMI can disrupt ovulation even in women who still have regular periods. The higher the BMI, the longer it typically takes to conceive. This isn’t just about ovulation: excess body fat alters hormone levels, increases inflammation, and can affect the uterine environment.
Being significantly underweight causes problems too, primarily by shutting down ovulation altogether. The body interprets low energy availability as a signal that it’s not a safe time to sustain a pregnancy.
Smoking damages eggs and reduces ovarian reserve in women, while lowering sperm count and motility in men. Heavy alcohol and caffeine intake have both been linked to longer time-to-pregnancy, though moderate caffeine consumption (one to two cups of coffee daily) doesn’t appear to be a significant factor for most people.
When No Cause Is Found
Up to 30 percent of couples going through a fertility evaluation receive a diagnosis of unexplained infertility. This label is given after standard testing shows at least one open fallopian tube, confirmed ovulation, and an adequate semen analysis. It doesn’t mean nothing is wrong. It means the standard tests didn’t catch the problem. Subtle issues with egg quality, sperm function, fertilization at the cellular level, or implantation can all fall below the detection threshold of routine workups.
Unexplained infertility can be frustrating precisely because there’s no clear target to fix. Treatment typically moves through progressively more intensive options, starting with medications that boost ovulation combined with timed intercourse, then intrauterine insemination, and potentially IVF. Many couples with unexplained infertility do eventually conceive, either with treatment or on their own, but the path often requires patience and a willingness to try multiple approaches.
What a Fertility Workup Actually Involves
If you’ve hit the timeline threshold for your age, a standard evaluation covers a few key areas. For the female partner, this includes bloodwork to check hormone levels and ovulation status, an AMH test to assess egg reserve, and an HSG or ultrasound to evaluate the uterus and tubes. For the male partner, a semen analysis is the essential first step.
These initial tests are relatively straightforward and can rule in or out the most common causes within a cycle or two. If results point to a specific issue, treatment can be targeted. If everything looks normal on paper, your doctor will likely discuss the unexplained infertility pathway and what options make sense given your age and how long you’ve been trying.