Weight and Infertility
Obesity is associated with a range of adverse health consequences. Widely recognized are the increased risks of cardiovascular disease, diabetes and some cancers. Obesity and low body weight can impact on reproductive function by causing hormone imbalances and ovulatory dysfunction. Abnormal weight is usually defined as a high BMI (kg/m2) of >25 and a low BMI of <20. High BMI has also been shown to adversely affect the outcomes of ART treatment. High body mass index also influences treatment outcomes of assisted human reproduction.
In the general population, a study was conducted on a total of 2527 cases of married women who had attempted to become pregnant for more than 1 year with no success because of ovulation infertility. Compared to women with a BMI of 20–21.9, women with a BMI of 24–25.9 showed a relative risk of infertility of 1.3and rising to 3.7 in women
with a BMI of >32.
In support of these findings, a study that investigated lifestyle factors in 2112 pregnant women found that increased time to conception was associated with a BMI of >25 and <19. Male BMI of >25 or<20 has also been associated with a reduction in sperm quality.
Obesity has been shown to decrease the probability of pregnancy for women undergoing ART. A large Australian study of 3586women who underwent ART found that pregnancy rates were halved for very obese women in comparison with women with abnormal BMI.
A national study of all IVF clinics in the Netherlands reported a 33% reduction in live birth rate for women on their first IVF cycle with a BMI > 27, compared to women with a normal BMI.
High BMI in women has also been associated with other adverse pregnancy outcomes such as gestational diabetes and hypertension.
The evidence for the effects of weight on reproduction from observational studies has given rise to a number of significant intervention studies. Lifestyle modification programs that include exercise have been shown to assist women to lose weight, improve their fitness, increase psychological well-being and improve reproductive functioning.
The results of an Australian study of 87 obese (BMI > 30) infertile women attending a weekly program to promote lifestyle changes demonstrate that a relatively small amount of weight loss (average of 6.5 kg) was associated with resumption of ovulation.
The women in this study attended a weekly program for 6 months that included an exercise component and education relating to diet and psychological issues associated with being overweight. Although the number of women taking part in the study was relatively low, the positive effects of participating in the program were outstanding. On average, the women lost 10.2 kg/m2, and at the beginning of the study, 80% of the women were an ovular and at the end of 6months 90% of these women were ovulating spontaneously. Of the 67 women who completed the study, 77.6% became pregnant and 67% achieved a live birth. The women who did not become pregnant either smoked, attended less than two-thirds of the sessions or had a BMI which remained 40.
G.F. Homan, M.Davies,R.Norman, The impact of lifestyle factors on reproductive performance in the general population and those undergoing infertility treatment: a review, Human Reproduction Update, Vol.13, No.3 pp. 209–223, 2007