The combined impact of maternal age and body mass index on cumulative live birth following in vitro fertilization

It is critical to evaluate the combined impact of age and body mass index on the cumulative likelihood of live birth following in vitro fertilization, as achieving a lower body mass index before infertility treatment often is recommended for women with overweight and obesity. It is important to consider whether achieving a particular body mass index, thus resulting in an older age at in vitro fertilization cycle start, is beneficial or harmful to the likelihood of live birth. To evaluate the combined impact of age and body mass index on the cumulative live birth rate following in vitro fertilization to inform when delaying in vitro fertilization treatment to achieve a lower body mass index may be beneficial or detrimental to the likelihood of live birth. This is a retrospective study using linked fresh and cryopreserved/frozen cycles from January 2014 to December 2015 from the Society for Reproductive Technology Clinic Outcome Reporting System, representing >90% of in vitro fertilization 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 in vitro fertilization cycles compared across age (years) and body mass index (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. 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 body mass index and age, and the miscarriage rate increased with increasing body mass index and age (linear trend P