Fertility improves most when you address the basics: body weight, diet, exercise habits, and exposure to common environmental chemicals. A woman in her early to mid-20s has a 25–30% chance of conceiving in any given month, but by age 40 that drops to around 5%. While age is the single biggest factor you can’t change, the factors you can change have a meaningful, measurable impact on your odds.
Why Body Weight Matters More Than You Think
Maintaining a BMI in the normal range (18.5 to 24.9) gives you the best foundation for conception. A large national study tracking over 100,000 IVF cycles found that live birth rates dropped steadily as BMI rose: 32.6% for normal-weight women, 29.4% for overweight women, 27% for women with class I obesity (BMI 30–35), and just 21.1% for women with a BMI of 35 or higher. That’s a roughly one-third reduction in success rates for women in the highest weight categories compared to normal weight.
Being underweight didn’t show a statistically significant reduction in that same study, but very low body fat is well established as a cause of irregular or absent ovulation. If your periods are irregular and your BMI is below 18.5, gaining even a small amount of weight can restore normal cycles. For both partners, the goal isn’t a specific number on the scale but getting into a range where your hormones function optimally.
The Mediterranean Diet and Conception Rates
If there’s one dietary pattern with strong evidence behind it for fertility, it’s the Mediterranean diet. Women who scored highest on Mediterranean diet adherence had a 50% clinical pregnancy rate compared to 29% among those who scored lowest. Across multiple studies, closely following this eating pattern was associated with 1.4 to 2.7 times higher odds of clinical pregnancy and up to 2.5 times higher odds of live birth.
The benefits come from several food groups working together. Fruits and vegetables provide antioxidants that support egg quality and maturation. Olive oil and fish (rich in omega-3 fatty acids) improve sperm parameters. Nuts and legumes, which supply folate, healthy fats, and plant-based protein, have been linked to better embryo development. Whole grains contribute fiber and B vitamins. The overall anti-inflammatory effect of this dietary pattern also appears to create a more favorable environment for embryo implantation.
You don’t need to overhaul your entire kitchen overnight. Shifting toward more vegetables, fish, olive oil, nuts, and whole grains while reducing processed foods and red meat moves you in the right direction.
Exercise: The Sweet Spot Between Too Little and Too Much
Moderate exercise supports fertility, but vigorous exercise can work against it. The threshold is surprisingly low. Women who did two hours of vigorous exercise per week were 16% less likely to conceive than sedentary women. At three to four hours per week, that gap widened to 27%. At five or more hours, the reduction hit 32%.
The mechanism is straightforward: intense exercise can suppress ovulation or shorten the luteal phase (the window after ovulation when a fertilized egg needs to implant). One study comparing regular runners averaging about 20 miles per week to sedentary women found that 58% of the runners had menstrual cycle abnormalities, including skipped ovulation, versus only 9% of sedentary women. Exercising to exhaustion was associated with 2.3 times the odds of infertility compared to taking it easy.
The good news is that moderate activity is protective. Exercising for 15 to 60 minutes at a comfortable pace was associated with lower odds of infertility than exercising for less than 15 minutes. The practical takeaway: keep moving, but if you’re trying to conceive, swap some high-intensity sessions for brisk walks, swimming, or yoga. “Vigorous” in the research means activity at 60% or more of your heart rate reserve, the kind that causes heavy sweating and makes it hard to speak more than a word or two.
What Men Can Do
Fertility is a two-person equation, and roughly a third of infertility cases involve male factors. Sperm quality responds to both supplements and lifestyle changes.
CoQ10, an antioxidant your body already produces, improved sperm motility in a study using 200 mg daily for six months. Zinc supplementation for three months increased both total normal sperm count and the percentage of sperm swimming forward effectively. Selenium, taken for about seven months alongside another antioxidant, led to significant improvements across all sperm measurements.
Heat is a direct enemy of sperm production. The testicles sit outside the body for a reason: they need to stay cooler than core body temperature. Laptop computers placed on the lap raise scrotal temperature, and research has shown a significant decrease in sperm motility from laptop heat exposure. Hot baths, saunas, and tight-fitting underwear have similar effects. If you’re trying to conceive, keep laptops on a desk, skip the hot tub, and choose looser-fitting boxers.
Alcohol and Caffeine
Alcohol has a clear, dose-dependent effect on fertility. Women who drank more than seven alcoholic drinks per week were 7% less likely to conceive after fertility treatment. When male partners drank at that level, chances of a live birth dropped 9%. Cutting back to a few drinks per week, or eliminating alcohol entirely during the preconception window, removes a modifiable risk.
Caffeine, on the other hand, appears far less concerning than many people assume. A Harvard study found that caffeine consumption by either partner didn’t affect the odds of pregnancy or live births. That said, most reproductive guidelines still suggest keeping intake moderate, generally under 200 to 300 mg per day (roughly two cups of coffee).
Reducing Chemical Exposures
Phthalates, a class of chemicals used to make plastics flexible, are endocrine disruptors that interfere with reproductive hormones at the cellular level. They can disrupt nuclear receptors, alter signaling pathways, and change gene expression related to reproduction. The problem is that phthalates are everywhere: plastic food containers, personal care products, vinyl flooring, and fragranced household items.
Practical steps to reduce your exposure include storing food in glass or stainless steel instead of plastic, avoiding microwaving food in plastic containers, choosing fragrance-free personal care products, and reading labels for ingredients like “diethyl phthalate” or simply “fragrance” (which often contains phthalates). These changes won’t eliminate exposure entirely, but they can meaningfully lower the amount circulating in your body within days to weeks.
Supplements for Women With PCOS
Polycystic ovary syndrome is one of the most common causes of irregular ovulation, and myo-inositol has become a well-studied option for women with this condition. In a meta-analysis, myo-inositol was nearly three times more effective than metformin at restoring regular menstrual cycles. The most commonly studied dose is 2 grams twice daily, often combined with 200 to 400 micrograms of folic acid.
For women undergoing fertility treatment, myo-inositol also appears to improve egg quality. One trial found that women taking 4 grams of myo-inositol daily for eight weeks before treatment had a pregnancy rate of 51%, compared to 24% in the comparison group. The supplement works by improving how cells respond to insulin, which in turn helps normalize the hormonal imbalances that prevent ovulation in PCOS.
Age and When to Seek Help
Age affects fertility more steeply than most people realize, particularly after 35. The decline isn’t just about egg quantity but also egg quality, which directly influences the chance of a chromosomally normal embryo.
Professional guidelines from the American Society for Reproductive Medicine recommend starting a fertility evaluation after 12 months of trying if you’re under 35, after 6 months if you’re 35 or older, and more immediately if you’re over 40. If you have a known medical condition associated with infertility, such as endometriosis, PCOS, or a history of pelvic infections, evaluation should begin right away regardless of age.
These timelines exist because earlier intervention in older age groups leads to better outcomes. Each month of delay matters more as you get older, and many causes of difficulty conceiving are treatable once identified.