Body mass index: impact on IVF success appears age-related.

Background: The objective of this study was to examine the effect of BMI on IVF outcomes.

Methods: This was a retrospective analysis of all patients undergoing IVF from 1st January 2005 to 1st March 2006 in a large private practice using a single IVF laboratory. The patients underwent standard protocols for controlled ovarian hyperstimulation and embryology parameters. The main outcome measure was clinical pregnancy rate.

Results: A total of 2167 fresh, non-donor IVF cycles were queried, but to minimize bias, only the first treatment cycle for each patient was analyzed (n = 1273). The data were examined by multiple regression models that included BMI and Age as main effects plus a BMI x Age interaction. When examined as a main effect, BMI did not appear to have a major effect on IVF outcome, but there was a significant BMI x Age interaction. At younger ages, a high BMI had a pronounced negative influence on fertility, but this effect diminished as the patient age increased. Clinical pregnancy rates decreased with increasing BMI and increasing Age.

Conclusions: In younger patients undergoing IVF, BMI has a significant negative impact on fertility that diminishes as patients reach their mid thirties. After Age 36, BMI has a minimal impact on fertility.