Optimal Weight for Fertility

How Much is Too Much? How Little is Too Little?

The issue of women's weight is a touchy subject in most circles and perhaps even more so among women who are having a hard time getting pregnant. Visit most fertility chatrooms or bulletin boards on the Internet and you're likely to find conversations that center around "fat-phobic" doctors, diets that enhance fertility while curbing body mass index, and all the related emotional distress that goes with the compounded struggle.

What's the truth of the matter? Are there really physicians out there who will take one look at a woman, size her up, and immediately pronounce that she must first lose (or less often, gain) weight before entering any fertility treatment plan? Is there really anything more to this question of female weight and its impact on fertility aside from societal judgement?

We spoke with physicians in the IntegraMed network for their take on the matter.

The Size-Fertility Connection

Dr. Celeste Brabec of Reproductive Resource Center of Greater Kansas City illustrates the size versus fertility issue: "Being either overweight or underweight can affect fertility, as can extreme exercise even without weight loss or low body fat. A normal body mass index, or BMI, is 19-24, a BMI of 25-29 is considered overweight, obese is 30-39, and extreme obesity over 39."

Body mass index is a tool, not an actual measurement, that provides a simple way to conceptualize a person's weight and relative health. It provides a good estimate of a person's weight adjusted for their height, and it tends to correlate with the percentage of fat on their body. It's important to understand that muscle mass and fat weigh differently, so BMI alone can never fully be translated to someone's health status.

{For more details on weight-related definitions and how to measure one's BMI, see this - http://www.cdc.gov/nccdphp/dnpa/obesity/defining.htm - and related webpages from the U.S. Centers for Disease Control.}

The connection that experts refer to can be generalized thus: fertility rates appear to be lower and miscarriage rates higher in women who are overweight. In fact, as Brabec points out, "Women with high BMIs appear to have lower pregnancy rates even with IVF." The physicians' comments indicate the importance of readers understanding the nature of statistics and the concept of fertility as a continuum. It's not the case that there is any one optimal weight or even BMI that will assure fertility or successful pregnancy.

The reasons for links between BMI and fertility aren't entirely clear, but most indications point to the fact that hormonal balance becomes disrupted when a body has more fat-related weight than is optimal for health.

"Fat makes hormones," explains Dr. David Hoffman of IVF Florida Reproductive Associates, "and these additional estrogens can then interfere with optimal hormone levels."

Similar hormonal disruption can occur in women who are seriously underweight, represented by a BMI of 19 or less. Surprisingly, under-weight women may have even more difficulty hearing that their weight is standing in the way of conception, since they are more likely to be rewarded by society, friends, and family for being thin. Suggestions by a fertility expert to gain weight may be a thin woman's first encounter with being told that her health is not optimal.

Research on more precise size-fertility connections is always under way. One relatively positive retrospective study of obese patients using IVF with donor egg pointed to the possibility that oocyte (egg) quality, not endometrium (uterine lining) quality, is a likelier cause of obesity-related poor pregnancy outcome (Fertility & Sterility, June 2005). More research is necessary to explore further the importance of maternal weight on endometrial receptivity and resulting conception and pregnancy issues.

Balance is Key

As with so many aspects of life, moderation is apparently important to optimizing fertility.

"It's all about making healthy lifestyle choices," says Dr. Hoffman. "As health professionals, we're interested in our patients' benefit overall, not just in helping them get pregnant."

Hoffman ventures that in the frequent societal discussions about weight, people often confuse the different terms used. He recommends keeping in mind that the term "morbid obesity" refers to someone who weighs two times their ideal body weight.

"Yes, there's a relationship between weight and fertility," says Hoffman, "but it's not a profound connection until we're talking about morbid obesity, which is a condition that is itself life-threatening."

Dr. Celeste Brabec of Reproductive Resource Center of Greater Kansas City offers some tips that are good, basic, and common sense for anyone trying to enhance their health, whether for weight loss, fertility or any other goal.

"A healthy diet composed of all food groups and a healthy exercise program are strongly advised. While cutting down on carbs may be sensible, particularly for women with PCO variants and insulin resistance, cutting down is not the same as cutting out, with the exception of pop and juice. Cutting out carbonated beverages (soda pop with sugar) and juice is safe, and can be a good place to start. Serving size is the key to the rest. Seek a formal nutritional consultation through your primary physician. Don't forget good sleep habits and other means of reducing stress."

Dr. Brabec adds, "All of our hormones interact with each other. Make healthy lifestyle decisions."

There is no documentable evidence of a particular weight loss plan, whether diet or exercise, that will ensure conception. On the other hand, there may be diets or physical activities that could be contraindicated for some individuals. Because every body varies, the best way to find out what's right for your body is to talk through the details with your personal physician.

A Matter of Good Health

The physicians we spoke with do not turn away patients because of their weight.

As Dr. Hoffman states plainly, "Being overweight is not a contraindication to getting pregnant." He urges that the emphasis in patient-physician communication on the matter should center on general health, rather than an ideal weight. "I was overweight as a child and had to watch my diet and exercise, so I have some idea of the struggle."

What about the concern of a woman's biological clock as compared to her need to optimize weight? Are women in their 30's and older told to take a year off from baby-making efforts so they can lose or gain weight? Hoffman recommends that his older fertility patients who may benefit from weight adjustment proceed with both efforts at the same time.