Risk of ovulatory infertility in relation to body weight.
Three hundred seventy-six infertile women in whom there was evidence of ovulatory dysfunction were compared to fertile controls to determine if being excessively under or overweight at the time of planned conception was associated with an increased risk of infertility. In nulligravid women (n = 204), body weight for height 85% or less than "ideal" was associated with a 4.7-fold increase in risk (95% confidence interval = 1.5 to 14.7) of infertility associated with ovulatory dysfunction. Nulligravid women who were 120% or more over their ideal weight were also at increased risk for ovulatory infertility (relative risk = 2.1, 95% confidence interval = 1.0 to 4.3). Neither association was seen among women who had been previously pregnant. The presence of abnormalities of endocrinologic reproductive function in underweight and overweight women argues that the associations we have noted in nulligravid women represent cause-and-effect relationships. If so, we estimate that 6% of primary infertility in which ovulatory dysfunction is present results from being excessively underweight, and another 6% from being excessively overweight.