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Exercise and Fertility: Are You Too Fit to Get Pregnant?

Woman Running Fertility Exercise

Photo: Pond5

When Dr. Andrew Toledo’s 32-year-old patient showed up at his office complaining of irregular periods and an inability to get pregnant two years ago, the Atlanta fertility specialist immediately asked about her exercise routine.

As he guessed, she’d spent the previous three months training hard for the Chicago Marathon. Even though she had recently completed several half-marathons, the increase in mileage had put just enough stress on her body to make her menstrual cycles go haywire. And if she didn’t ovulate regularly, she wouldn’t be able to get pregnant.

So Toledo, chief executive officer at Reproductive Biology Associates, gave her the speech he’d given to the growing number of female athletes he’d seen over the years: “If you really want to get pregnant, you’ve got to cut back on exercise. You can’t do both,” he said.  Since he was also a runner and had competed in the Atlanta Marathon in 2002, he also gave her the option of taking a break from baby-making until the race was over. 

She chose to stop training and became pregnant a couple months later. “It can happen quickly,” he explained. “If you don’t take your body off a cliff, it will heal itself.”

Too Much of a Good Thing?

“Exercise is a great thing for anyone trying to get pregnant …The problems arise when you take it to the extreme.”

At 5’5” and 120 pounds, Toledo’s patient was on the lean side, but she wasn’t technically underweight (defined as having less than 20 percent body fat), a known cause of infertility among elite athletes, such as distance runners, ballet dancers and gymnasts. In fact, about six percent of infertility cases are due to being underweight, according to the American Society for Reproductive Medicine.

Rather, she fit into a murky but expanding category: healthy women who push their bodies just far enough that they disrupt their delicate hormonal balance, and their brain stops sending a signal to the ovaries to send down an egg to fertilize. The increased recognition of the relationship between endurance exercise and infertility brings up the question: Can being too fit hurt your chances of getting pregnant?

Of course, doctors are reluctant to discourage women to exercise, considering that six percent of infertility cases are caused by obesity. “Exercise is a great thing for anyone trying to get pregnant,” explains Toledo. “It improves blood flow to the uterus and ovaries, and makes you feel good. The problems arise when you take it to the extreme. You’re subjecting your muscles and joints to constant pounding, and the body starts to break down.” All the energy your body would have dedicated to getting pregnant gets redirected to healing injuries.

A Norwegian population-based survey of nearly 4,000 women under 45 found a clear link between exercise intensity and fertility. Women who were active most days were more than three times more likely to have fertility problems than inactive women. And those who exercised to the point of exhaustion were more than twice as likely to be infertile than those who engaged in less strenuous activities, according to results published in Human Reproduction.

Men who want to be dads soon shouldn’t sign up for the next Ironman, either. Research shows that over-exercising can harm sperm production. That’s not to mention the recent Spanish findings that male cyclists who rode more than 180 miles a week had more strangely shaped swimmers. All that saddle time has been shown to cause unfriendly friction and overheated testes — hardly ideal conditions for optimal fertility.

Body Shut-Down

It’s often a combination of genetics, not getting enough calories and being significantly underweight that causes women to experience ovulation problems.

When your body is under so much physical stress, especially if you’re not eating enough to compensate for the energy you’re using, it goes into a starvation state. “The brain figures it’s not a good time to have a baby, and the body and reproductive hormones go into shut-down mode,” explains Karine Chung, M.D., a reproductive endocrinologist at University of Southern California Fertility in Los Angeles, who writes about the effects of exercise on reproduction. “There are less extreme versions of this in people who aren’t that underweight but have intense workouts multiple times a week.” If they’re missing periods, a condition known as amenorrhea, they’re at risk for infertility. Over time, the lack of estrogen that’s usually produced as part of menstruation, can have long-term health consequences, such as osteoporosis and eventually heart attacks.

Exercise itself doesn’t cause infertility, stresses Raul Artal, M.D., chair of the department of obstetrics, gynecology and women’s health at St. Louis University. It’s often a combination of genetics, not getting enough calories and being significantly underweight that causes women to experience ovulation problems. In these cases, their cycles will become more regular once they reach a normal BMI (more than 111 pounds for a 5’5” woman). “As long as they have an adequate body weight, most women will ovulate just fine, even on marathon weekend,” he says. 

Fertility Test

Photo: Pond5

Finding the Sweet Spot 

Hoping to get pregnant but don’t want to slow down your training? Here are some tips to help you do both:

1. Track your menstrual cycle.
If you notice a significant change in the time in between your periods, especially if it coincides with your ramped-up training schedule, that may be a sign it’s time to slow down, says Chung. Your period should arrive every 28 to 30 days on average, however it can range from 21 to 35 days. “If it’s any shorter or longer than that, I’d be worried you’re not ovulating,” she says.

2. Pee on a stick.
It’s a good idea to monitor your ovulation cycles to make sure your body is working as it should. Those drugstore tests will detect the surge of luteinizing hormone in your urine, which takes place right before ovulation, says Toledo.

3. Consume enough calories.
A 135-pound female with 20 to 25 percent body fat who runs an hour a day at moderately high intensity would need to eat a minimum of 1900 to 2000 calories a day to maintain fertility, explains Enette Larson-Meyer, PhD, associate professor of human nutrition at the University of Wyoming. Make sure your diet has adequate levels of fat and protein. And go easy on fiber, which in large amounts can interfere with ovulation.

4. See a fertility specialist.
This is a no-brainer if you’re having sexual intercourse regularly and haven’t gotten pregnant within a year (or six months, if you’re over 35). Your doctor can help pinpoint any potential roadblocks and, in some cases, might prescribe medication to help you ovulate.

5. Consider freezing your eggs.
If making babies doesn’t fit into your training schedule, there’s also the option of putting some eggs on ice until you’re ready to conceive. The choice is a personal one, but if that’s the route you chose, be sure to freeze your eggs when your fertility is at its prime, ideally before turning 35.  

Most athletes have no problems getting pregnant. But just as you prepare your body for baby-making by taking folic acid and cutting back on drinking, keeping a moderate exercise schedule may be another item to add to your checklist.

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