Why Some Women Have So Much More Trouble Getting Pregnant Than Others

You’re likely no stranger to this news: “Age is the most consistent gauge of a woman’s fertility,” says Styer. “If you’re younger, you have higher quality and quantity of eggs.” Think about it: You’re born with all of the eggs you’ll have and, over time, that number declines.

What doctors consider peak fertility varies, though. While Styer says it’s between ages 20 and 24, Mary Jane Minkin, M.D., a clinical professor of obstetrics and gynecology at Yale University School of Medicine suggests it’s between ages 18 and 30. “Fertility significantly declines after 40 with some decline at about 35,” she says. “But I never discourage women about it—the only time I really kick butt and say, ‘OK, let's go for it now!’ is in women over 40.”

After 40, docs worry about issues like a higher risk of chromosome abnormality, says Elizabeth Ginsburg, M.D., the medical director of assisted reproductive technologies at Brigham and Women’s Hospital in Boston.

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By now, you know smoking is a big no-no. But allow us to drive it home: “Smoking causes a loss of eggs and makes eggs less likely to fertilize,” says Ginsburg. And if you do get pregnant, as a smoker you’re at an increased risk of miscarriage, she says. Minkin explains that a cigarette habit ages the ovaries—and that smokers tend to go through menopause a year or two earlier. 

Research suggests that there’s a big connection between weight and infertility. That’s why most docs urge their patients to maintain a healthy bodyweight. “The more normal someone’s body is, the more likely they are to not have an infertility problem,” says Ginsburg. While obesity has been linked to infertility, the same issue seems to crop up if you clock in fairly underweight, too. Some marathoners and long-distance runners tend to have decreased fertility because of a lower percentage of body fat, says Minkin. The issue likely boils down to hormones, which can be impacted by body-fat levels and thus affect signaling between your pituitary gland, which secretes hormones to various parts of the body, and your ovaries.

Randomly getting busy likely isn’t your best plan of action if you want a baby. “There’s between a 12- and 24-hour window when an egg can be fertilized during intercourse,” says Styer. So your best bet is to have sex before and around ovulation, which happens two weeks before your period. Try every few days around that time, suggests Ginsburg. An ovulation predictor kit is worth considering, too—they can be super helpful in making sure you're hitting your most fertile time.

RELATED: 11 Things You Should Know if You're Considering Freezing Your Eggs 

Issues like endometriosis—when tissue similar to the uterine lining grows outside of the uterus—can increase your risk of infertility, says Ginsburg. So can Polycystic Ovarian Syndrome (PCOS), an endocrine disorder, which can alter hormonal signals. A history of pelvic inflammatory disease (PID) can also play a role by blocking the fallopian tubes with scarring, says Minkin. “One episode of PID decreases fertility about 10 percent, two episodes by about 25 percent, and three episodes by about 50 percent,” she says. So if you’re not in a 100 percent mutually monogamous relationship, make sure you’re always using a condom. “You do not want to get chlamydia or gonorrhea,” says Minkin. And if you think (or know) you have any of these conditions, make sure to touch base with your ob-gyn.