An obese woman's likelihood of conceiving steadily decreases as her body mass index (BMI) increases, according to a study by Dutch researchers (van der Steeg JW et al. Hum Reprod.
doi:10.1093/humrep/dem371 [published online ahead of print December 11, 2007]).
The prospective cohort study involved 3029 subfertile ovulatory women and their partners, who were followed up until pregnancy or the start of fertility treatment within 12 months. The investigators found that compared with women who had a BMI between 21 and 29, women with a BMI between 30 and 35 had a 4% decrease in conception rates for every BMI unit increase.
Stephenson J. Obesity and Fertility. JAMA. 2008;299(3):279. doi:10.1001/jama.299.3.279-d