Fertility depends on a surprisingly short list of factors you can actually control: body weight, nutrient status, sleep, physical activity, chemical exposures, and timing. Whether you’re trying to conceive now or planning ahead, optimizing these areas gives you the strongest biological foundation. Here’s what the evidence says works, and how to put it into practice.
Get Your Weight Into the Fertile Range
Body weight is one of the most powerful levers for fertility because it directly controls hormone production. A BMI between 18.5 and 24.9 is considered the optimal range for conception. Outside that window, things shift quickly.
A BMI above 30 increases the risk of abnormal ovulation and irregular menstrual cycles. Excess body fat produces extra estrogen, which can confuse the hormonal signaling that triggers egg release each month. On the other end, a BMI below 18.5 often leads to irregular or absent periods, meaning ovulation may not be happening at all. Women who are underweight also face a higher risk of preterm birth if they do conceive. For men, excess weight is linked to lower testosterone and reduced sperm quality. Even modest weight changes in either direction, losing 5 to 10 percent of body weight if overweight, or gaining a few pounds if underweight, can restore more regular ovulation and improve sperm production.
Exercise at the Right Intensity
Moderate exercise improves fertility. Women who exercise 30 minutes or more daily have a reduced risk of infertility related to ovulation problems. The general target is 150 minutes per week of moderate-intensity activity, the kind where you break a sweat and feel winded but can still speak in short phrases. That works out to about 30 minutes, five days a week.
The benefit has a ceiling, though. More than an hour of vigorous exercise a day can suppress the hormones that drive ovary function, potentially causing ovulation to stop altogether. The risk increases with both duration and intensity. If you’re a normal weight, keep workouts to an hour or less daily. If you’re underweight and exercising five or more days a week, cutting back to three sessions may help. If you’re overweight, a longer routine is beneficial: aim for 60 minutes of cardio five days a week plus 30 minutes of strength training three times a week.
Protect Sleep to Protect Egg and Sperm Quality
Your body produces melatonin during sleep, and melatonin does far more than regulate your sleep cycle. It acts as a potent antioxidant inside the ovaries, protecting eggs from oxidative damage during maturation. The concentration of melatonin in follicular fluid (the liquid surrounding a developing egg) is directly associated with oocyte maturation rate and embryo quality.
Oxidative stress is one of the primary causes of poor egg quality. It reduces both the maturation rate and the fertilization rate of eggs, lowering the chance of a full-term pregnancy. Melatonin and its byproducts neutralize free radicals in the reproductive environment, shielding both eggs and early embryos. Studies in fertility clinics have shown that higher melatonin levels lead to more mature eggs collected and more good-quality embryos. The practical takeaway: consistent sleep of seven to nine hours in a dark room supports your body’s natural melatonin production. Irregular sleep schedules, night-shift work, and blue light exposure before bed all suppress it.
Build Your Nutrient Foundation
Start a prenatal vitamin before you start trying to conceive, ideally at least one to three months ahead. Folate is the nutrient most people know about, but two others are commonly overlooked. The recommended intake for iodine during pregnancy is 220 mcg per day, and many prenatal vitamins don’t contain enough (or any). Iodine is essential for thyroid function, which directly regulates ovulation. Choline, with a recommended intake of 450 mg during pregnancy, supports early brain development and placental health. Most women get far less than that from food alone.
For men, antioxidant supplements have strong evidence behind them. L-carnitine, taken at 1 to 3 grams per day for three to six months, improves sperm quality, supports healthy hormone levels, and reduces oxidative damage to sperm cells. It works by enhancing mitochondrial function, essentially improving the energy production system that sperm depend on to move effectively. It also activates the body’s own antioxidant defense enzymes. CoQ10 operates through a similar mechanism, supporting cellular energy in sperm. These supplements don’t work overnight; plan for at least three months, since a full cycle of sperm production takes roughly 74 days.
Reduce Exposure to Hormone-Disrupting Chemicals
Endocrine-disrupting chemicals are found in plastic bottles, food containers, cosmetics, food preservatives, pesticides, and even toys. The two most studied are BPA (bisphenol A) and phthalates, both used as plasticizers in thousands of products. Their effects on fertility are well documented and worth taking seriously.
BPA mimics estrogen in the body. Exposure has been linked to disrupted egg development, accelerated loss of ovarian follicles, decreased egg survival, and a higher risk of PCOS. Phthalates are associated with implantation failure and lower pregnancy rates. Parabens, commonly found in lotions and shampoos, have been linked to elevated estrogen levels in premenopausal women, which can throw off the hormonal balance needed for ovulation.
You can reduce your exposure with a few targeted swaps. Use glass or stainless steel containers instead of plastic, especially for hot food or liquids (heat accelerates chemical leaching). Choose fragrance-free personal care products, since “fragrance” on a label often contains phthalates. Avoid microwaving food in plastic. Wash produce to reduce pesticide residue, or choose organic for the items you eat most. These aren’t extreme measures, and they address chemicals that directly interfere with egg quality, embryo implantation, and hormone regulation.
Understand the Numbers: Sperm and Age
If a semen analysis is part of your fertility workup, it helps to know what the thresholds mean. The World Health Organization’s reference values represent the 5th percentile among men whose partners conceived within 12 months. In other words, these are the lower boundaries of normal, not the ideal. Sperm concentration should be at least 16 million per milliliter. Total motility (the percentage of sperm that are moving) should be at least 42 percent, with 30 percent showing forward, progressive movement. Normal shape (morphology) only needs to hit 4 percent, a number that surprises most people but reflects how strict the grading criteria are.
For women, age is the single strongest predictor of fertility, and the decline is steeper than most people expect. Fertility begins to drop noticeably after 32 and more sharply after 37. This isn’t about overall health; it reflects the number and chromosomal quality of remaining eggs. A healthy 40-year-old has significantly fewer viable eggs per cycle than a healthy 30-year-old, regardless of fitness level or lifestyle. This doesn’t mean conception is impossible at later ages, but it does mean that the other factors in this article become more important with each passing year. If you’re over 35 and have been trying for six months without success, that’s a reasonable point to seek a fertility evaluation rather than waiting the standard 12 months.
Timing Intercourse to Your Fertile Window
Ovulation typically occurs about 14 days before the start of your next period, not 14 days after the start of your last one (an important distinction for anyone with irregular cycles). The fertile window spans roughly six days: 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 is viable for only 12 to 24 hours after release.
The most effective approach is having intercourse every one to two days during the fertile window rather than trying to pinpoint a single day. Ovulation predictor kits detect the hormone surge that happens 24 to 36 hours before egg release, giving you a useful heads-up. Tracking basal body temperature can confirm that ovulation occurred but only after the fact, so it’s more helpful for understanding your cycle over several months than for timing a specific attempt. Cervical mucus that resembles raw egg whites, clear, stretchy, and slippery, is another reliable signal that ovulation is approaching.