LAUSR

BACKGROUND It is critical to evaluate the combined impact of age and body mass index (BMI) on the cumulative likelihood of live birth following in vitro fertilization (IVF), as achieving a lower BMI prior to infertility treatment is often recommended for women with overweight and obesity. It is important to consider whether achieving a particular BMI, thus resulting in an older age at IVF cycle start, is beneficial or harmful to the likelihood of live birth. OBJECTIVES To evaluate the combined impact of age and BMI on the cumulative live birth rate following IVF, in order to inform when delaying IVF treatment to achieve a lower BMI may be beneficial or detrimental to the likelihood of live birth. STUDY DESIGN This is a retrospective study using linked fresh and cryopreserved/frozen cycles from 1/2014-12/2015 from the Society for Reproductive Technology Clinic Outcome Reporting System, representing >90% of IVF cycles performed in the United States. The primary outcome was live birth as measured by cumulative live birth rate. Secondary outcomes included implantation rate, clinical pregnancy rate, and miscarriage rate. Poisson and logistic regression were used to calculate risk and odds ratios with 95% confidence intervals to determine differences in implantation, clinical pregnancy, and miscarriage, as appropriate, among first fresh IVF cycles compared across age (y) and BMI (kg/m2) categories. Cox regression was used to calculate hazard ratios with 95% confidence intervals to determine differences in the cumulative live birth rate using fresh plus linked frozen embryo transfer cycles. RESULTS There were 51,959 first fresh cycles using autologous eggs and 16,067 subsequent frozen embryo transfer cycles. There were 21,395 live births, for an overall cumulative live birth rate of 41.2% per cycle start. The implantation rate, clinical pregnancy rate, and cumulative live birth rate decreased with increasing BMI and age, and the miscarriage rate increased with increasing BMI and age (linear trend p<0.001 for all). BMI had a greater influence on live birth at younger ages as compared to older ages. CONCLUSIONS Age-related decline in fertility has a greater impact than BMI on the cumulative live birth rate at older ages, suggesting that taking time to achieve lower BMI prior to IVF may be detrimental for older women with overweight or obesity. Delaying conception to lose weight prior to IVF should be informed by the combination of age and BMI.