The latest evidence supporting this is in an article in the February 2010 edition of Fertility & Sterility looking at the outcomes in different groups based on BMI (body mass index as kilograms per square meter). They compared lean (<20 kg/m2); normal (20–24.9 kg/m2); overweight (25–29.9 kg/m2); and obese (≥30 kg/m2) women in 6500 IVF cycles. Although there was no difference in insemination procedure, fertilization rate, day of transfer, mean number of embryos transferred and cryopreserved embryos, percentage of blastocyst transfers, or embryo quality on day 2 and 3 among groups, pregnancy and live birth rates were reduced progressively with each category of increase in BMI. In addition, the cumulative pregnancy rate after four IVF cycles was reduced as BMI increased.

This confirms other studies that being obese or even just overweight overweight has a negative effect on IVF success.