Can you be too fit to conceive?

As female athletes take on harder training regimens with the goal of attaining leaner, stronger, and healthier bodies, they could actually be derailing their chances of getting pregnant.

For most women who wish to conceive, low and moderate exercise can help their chances by increasing blood flow to the pelvic region and decreasing stress levels. But it’s when they “push themselves to the extreme end of fitness” that problems can arise, says Robert Gustofson, M.D., a reproductive endocrinologist at the Colorado Center for Reproductive Medicine who has extensive experience working with professional athletes.

The factors at play

One major thing to consider when discussing exercise and fertility is weight, since abnormal body weight is the culprit for 12 percent of infertility cases, according to the American Society of Reproductive Medicine. And being underweight contributes to just as many cases of infertility as does being obese, with each group accounting for six percent, according to epidemiological data.

“We like to see a BMI range between 18.5 and 25. As you start getting below 18.5 and above 25, pregnancy rates are definitely compromised,” says Gustofson. But just as BMI has shortcomings in telling the whole story of weight distribution, it also provides an incomplete picture of what’s going on in a woman’s body, especially in a very fit woman’s body, and her ability to conceive. That’s because BMI doesn’t factor in the breakdown between muscle and fat. So while an extremely fit athlete may have a normal BMI due to large amounts of muscle, she may actually have too little body fat (which stores estrogen) to support pregnancy. Because of this, body fat percentage is another important indicator of fertility.

“At least 17 to 19 percent body fat is ideal for most, though there’s no exact number as every woman is different,” says Gustofson. “But, this is the level above which most women have the best chances of pregnancy.” (Percent body fat above above 25 to 30 percent is usually associated with obesity, which carries a difference set of risks, he adds.)

The problem with both low BMI and low body fat is that they put women at increased risk for having irregular or absent periods (a condition called amenorrhea). “This occurs due to dysfunction of the hypothalamus, an endocrine gland which exerts control over the pituitary gland in the brain that controls hormone production from the ovary,” explains Mark W. Surrey, M.D., co-founder and medical director of the Southern California Reproductive Center and clinical professor in the Department of Obstetrics and Gynecology at the David Geffen School of Medicine at UCLA.

Amenorrhea goes hand in hand with anovulation, which is when ovaries fail to release an oocyte (egg) during a menstrual cycle, says Surrey. “Chronic anovulation is a common cause of infertility,” he says.

However, women who experience exercise-induced amenorrhea and anovulation can still conceive, though not naturally. “You’ll need medication to induce ovulation,” says Gustofson. Though the first course of action would be to try and fix the underlying cause, often achieved just by cutting back on workouts in order to increase BMI and body fat.

How extreme is too extreme

There are no one-size-fits-all guidelines over what constitutes too much exercise when it comes to fertility, says Surrey, since each woman’s particular circumstances (BMI, body fat percentage, and diet) needs to be taken into account. “Athletes who train at a high intensity but have sufficient nutrient intake and body fat percentage may continue to ovulate normally and remain fertile,” says Rebecca Fett, science researcher and author of It Starts with the Egg: How the Science of Egg Quality Can Help You Get Pregnant Naturally, Prevent Miscarriage, and Improve Your Odds in IVF.

A huge cautionary red flag, however, is if your menstrual cycle isn’t regular. “Sometimes I’ll see professional athletes and they’ll know that if they increase their training to a certain level, they’ll lose their periods,” says Gustofson.

As a general rule, though, Gustofson recommends a minimum of 30-minute workouts at least three days a week, but to not overdo it beyond one-hour workouts more than six days a week if you’re actively trying to conceive.