Introduction: This seminal study describes infertility and menstrual dysfunction in women practicing strict weight control. While it was well known that weight loss of more than 15% of ideal body weight (IBW) is linked to amenorrhea and other metabolic abnormalities, this study investigated less marked weight loss in women who are otherwise healthy.
Methods: The study involved 47 women who practiced strict weight control and had unexplained infertility (n=29) or had amenorrhea but were not trying to conceive (n=18). On average, the women were between 89%-91% of ideal body weight. Most of the 29 women with unexplained infertility (93%) actually had abnormalities in menstrual cycles as measured using basal body temperature (BBT) upon further testing. The women were asked to follow a dietary regimen designed to reach achieve ideal body weight.
Results: Eleven women (3 in the infertile group and 8 in the amenorrhea group) withdrew from the study, stating that they did not believe that their weight control practices were the cause of their reproductive issues. The remaining 26 women with infertility and 10 women with menstrual disorders followed the dietary regimen, and reached within 95% of their IBW. Nineteen of the 26 women with infertility (73%) became pregnant after weight gain without any other intervention. In addition, 9 out of 10 women with amenorrhea (90%) resumed menstruation after weight gain. In addition, the authors found an association between percentage of IBW and gonadotropin ratio (luteinizing hormone: follicle stimulating hormone).
The authors noted that the women with infertility were “highly motivated” to gain weight once they were told that their weight control practices may be the cause of their inability to become pregnant. In contrast, the women with amenorrhea (who did not want to become pregnant) were “not motivated” to gain weight.
Conclusion: In women who were underweight from following strict diet/exercise regimens and had unexplained infertility or amenorrhea, weight gain to within 5% of IBW allowed nearly three-fourths of the 26 women with infertility to conceive and nearly all of women with amenorrhea to resume menstruation.
Bates GW, Bates SR, Whitworth NS. Reproductive failure in women who practice weight control. Fertil Steril. 1982;37(3):373-378.
Commentary by Tamara L Wexler MD, PhD
Tamara L. Wexler, MD, PhD, is an endocrinologist specializing in reproductive and neuroendocrinology, and an Attending in Medicine, Massachusetts General Hospital, Boston, MA.
Bates and colleagues studied a small group of women on diets for weight control. It had previously been established that weight loss to 15% IBW was associated with amenorrhea. The authors sought to look at lesser degrees of weight loss (5%-10% IBW), and the result of dietary intervention designed to lead to moderate weight gain.
A majority of the cohort had unexplained fertility at the outset (n=29, who did not report amenorrhea.) The remainder of the 47 women studied had menstrual irregularities, lower percent IBW of 89%, and were not seeking fertility. Here, we focus solely on the 29 women with unexplained infertility, all of whom were seeking pregnancy. These 29 women had IBW averaging 91%; average age was 28.5 years. Average infertility was greater than 4 years (range 1-9 years), and all but one of these women had previously undergone workup for infertility without identifiable cause. Most of the women (23 of the 29) were nulliparous. None of these women were deemed to have anorexia at the time of the study, though one reported a history of anorexia.
Measurements in addition to determination of percent of IBW included serum hormones and basal body temperature (BBT). All but three of the women in the “unexplained infertility” group had regular menses. However, based on BBT measurements, the authors felt the majority did in fact have some type of menstrual cycle abnormality (62% with a short luteal phase, 21% with irregular menses, 10% without menses, and 7% deemed to have entirely normal menses.) Of note, short luteal cycles were established on the basis of BBT—menses were regular in these women.
Intervention consisted solely of attempted weight gain at rate of 0.5 lb per week, under supervision of a dietician. Most of the women (26 of the 29) elected to participate. Following intervention, menstrual cycles were deemed to be normal in the majority of women (8% short luteal phase; 8% irregular menses; no amenorrhea; 84% normal menses.) Nineteen of these 26 women (73%) then conceived, although 4 experienced first trimester abortions (term used by authors—presumably miscarriages). Average weight gain in the 19 women was 8.2 lbs.
Weight loss and percent body fat under threshold have been associated with secondary amenorrhea (as has exercise). Based on BBT measurements—but not measurements of serum hormone levels or endometrial thickness—the authors postulate that a luteal phase defect is associated with lower percent IBW, and is largely corrected with weight gain.
This is a single-arm interventional study, with no control group or blinding. The group studied had all been identified as having infertility and referred to a reproductive endocrinology clinic. Study limitations also include the absence of progesterone level measurements to determine ovulation.
The importance of this 1982 study lies demonstrating the impact of moderate weight gain in promoting spontaneous conception in women with unexplained infertility and even mild degrees of underweight. Women need not look malnourished (the authors comment that women in the unexplained infertility cohort appeared “normal”) nor have obviously irregular menses to be suffering the effects of lower body weight on fecundity, and moderate weight gain may be sufficient to restore fertility.