Lose a few or gain a few to increase your chances.
Just past my 33rd birthday, at my annual ob-gyn visit, I casually mentioned that my husband and I were thinking about trying to get pregnant during the next year or so. “If I were you,” my doctor responded, “I’d think about putting on a few pounds ahead of time.”“Why?” I asked. “Is it better for the baby if you gain some weight before you get pregnant?”“No,” she answered, “I think you’d have a better chance of getting pregnant if you weren’t quite so thin.”
When I repeated this story to a friend recently, she told me a similar tale, but with a flip side: her doctors had suggested she take off a few pounds before attempting to get pregnant at age 37.
No one had ever told us that before. But it turns out that we may be part of a growing group in America: those whose body weight—either too low or, even more commonly, too high—is hurting their fertility. In fact, some experts now believe that a woman’s weight may be a factor in up to 10 percent of infertility cases. And that how much you weigh years before you think about having a baby may also make a difference.
The Biology of Body Fat
Amid all the hoopla over high tech treatments, “the basic connection between body fat and hormone balance is being ignored,” states reproductive endocrinologist G. William Bates, M.D., whose studies on the subject date back to the 1980s. A clinical professor at Vanderbilt University, Dr. Bates and his colleagues came to a few simple conclusions: Not only did many high-level women athletes cease menstruating, but significant numbers of “fashionably thin” women, not just anorexics, may have had their periods but actually stopped ovulating. Along with others, the researchers also observed a paradox: Women who were overweight—and not just those who were obese—often experienced problems getting or staying pregnant as well.
The reason: Body fat literally communicates with the brain. Intercourse may be the sexy part of conception, but the beginning is, as the saying goes, all in your head.
“We now know that fat cells produce a weak form of estrogen, one reason that men who are fat gain breasts,” explains Gary W. DeVane, M.D., of the Center for Infertility and Reproductive Medicine, Orlando, Florida. “The problem is that a low level of circulating estrogen is the brain’s signal to pump out other hormones that prod the release of new eggs from follicles in the ovaries. In a woman who has too much body fat, the brain can be fooled into thinking that the hormones are all doing their jobs, with the result that the egg-release cycle doesn’t get under way.”
Other problems that are caused by or often accompany excess weight include high levels of androgens (so-called male hormones that are actually secreted by both sexes) and insulin resistance, along with a condition known as polycystic ovarian syndrome, or PCOS, in which many cysts develop from ovarian follicles that fail to rupture and release eggs. PCOS is considered one of the most common hormonal disorders among women. “Although true polycystic ovarian disease usually develops at puberty and can cause weight gain, the syndrome can come on later in life as a result of weight gain,” explains Michael R. Soules, M.D., professor and director of reproductive endocrinology and infertility, department of obstetrics and gynecology, University of Washington, Seattle.
“A woman with PCOS can sometimes have a few cycles in which an egg is successfully released, but the defining symptoms are irregular periods and lack of ovulation. No egg release means no possible pregnancy.”
{loadposition frboost}
Women who are too thin also suffer from mixed signals to the brain. In this case, the problem seems to occur when the hypothalamus, the brain’s central hormone command structure, receives a signal that there is too little body fat (and/or estrogen) to support a pregnancy. Although the precise chemical pathway is still unknown, says Robert Rebar, M.D., executive director of the American Society for Reproductive Medicine, the result is that the brain doesn’t send the proper amount of GnRH (gonadatrophin releasing hormone) to the pituitary gland to stimulate the subsequent release of the follicle- and egg-stimulating hormones LH and FSH. A study recently published in The New England Journal of Medicine suggests that leptin, a metabolic hormone that made headlines in anti-obesity research and is depleted during fasting, may also play a role. If a woman is somewhat underweight, she may be secreting some hormones but not in the precise amounts or timing needed to insure conception and a healthy pregnancy. “We now know that all hormones are secreted in pulses,” says Dr. Rebar, who is also a clinical professor at the University of Alabama, Birmingham. “The body is finely tuned to following these rhythms for ovulation to occur.”
Complicating matters even more: each woman’s body has its own ideal weight range for conception.
Being Overweight Puts Fertility at Risk
Generally speaking, experts define “normal weight” as a BMI (body mass index) of 18.5 to 24.9. Overweight is a BMI between 25 and 29, and a person is considered obese when she has a BMI of 30 and over. The surprising conclusion of a 2002 analysis of the famed Harvard Nurses’ Health Study 2: Gaining weight, even into the high-normal range (a BMI of 24 or above) could begin to significantly compromise a woman’s fertility.
“Ours was one of the first studies to look at the regular habits of average American women. Essentially, what we found was a U-shape curve, with higher risks of infertility among women who were either very lean or even modestly overweight,” explains lead researcher Janet Rich-Edwards, MPH, of the department of ambulatory care and prevention, Harvard Medical School /Harvard Pilgrim Health Care.
“In our country, there aren’t that many women who have a BMI less than 20, but there are a whole lot with a BMI of 25 or more. The fact that there are so many women who are overweight means that while roughly 12 percent of what’s classified as ovulatory infertility could be attributed to underweight, 25 percent of ovulation-related infertility could be due to overweight.”
- 1
- 2
