The impact of increasing body mass index on in vitro fertilization treatment, obstetrical, and neonatal outcomes

Background: Citing the risks of administering anesthesia to patients with obesity, few fertility centers offer in vitro fertilization as a treatment modality for patients with body mass indexes ≥40 kg/m². Although previous studies have assessed clinical pregnancy and cumulative live birth rates in patients who spontaneously conceive with body mass indexes ≥50 kg/m², there is a paucity of in vitro fertilization, obstetrical, and neonatal outcome data in patients with severe obesity who conceive after in vitro fertilization.

Objective: This study aimed to evaluate the impact of increasing body mass index on in vitro fertilization, obstetrical, and neonatal outcomes in patients with obesity undergoing in vitro fertilization.

Study design: This was a retrospective cohort study within an academic fertility center including 2069 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycles from January 1, 2012 to April 30, 2020; this cohort was used to determine in vitro fertilization treatment outcomes. A second embedded cohort of 867 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycles that resulted in ongoing clinical pregnancies and deliveries within a single tertiary hospital system was used to determine pregnancy, maternal, and neonatal outcomes. All patients with a body mass index ≥40 kg/m² underwent consultation with a maternal-fetal medicine specialist before starting treatment and a preoperative evaluation with an anesthesiologist before oocyte retrieval. Cycles were grouped by body mass index at cycle start (30-34.9, 35-39.9, 40-44.9, 45-49.9, and ≥50 kg/m²). Log-binomial regression and Poisson regression with an offset were fitted with body mass index of 30 to 34.9 kg/m² as the reference group, adjusting for potential confounders including oocyte age, patient age, embryo quality, transfer type, and coexisting comorbidities. The primary outcome was live birth rate. Secondary outcomes included fertilization rate, blastulation rate, miscarriage rate, incidence of preeclampsia with severe features, gestational diabetes, labor induction, cesarean delivery, preterm delivery, and birthweight.

Results: There were 2069 fresh in vitro fertilization/intracytoplasmic sperm injection and frozen embryo transfer cycle starts from January 1, 2012 to April 30, 2020. Of these, 1008 cycles were in the 30 to 34.9 kg/m² group, 547 in the 35 to 39.9 kg/m² group, 277 in the 40 to 44.9 kg/m² group, 161 in the 45 to 49.9 kg/m² group, and 76 in the ≥50 kg/m² body mass index group. Live birth rate was not significantly different between groups. The body mass index ≥50 kg/m² group was significantly more likely to experience preeclampsia with severe features when compared with the 30 to 34.9 kg/m² body mass index group (absolute risk reduction, 2.75; 95% confidence interval, 1.13-6.67). Fertilization rate, blastulation rate, miscarriage rate, incidence of gestational diabetes, labor induction, cesarean delivery, preterm delivery, and neonatal birthweights were not significantly different between groups.

Conclusion: Among patients with body mass indexes from 30 to 60 kg/m² who conceived via in vitro fertilization and received comprehensive prenatal care at a tertiary care hospital, in vitro fertilization, obstetrical, and neonatal outcomes were largely comparable. These data support a collaborative care approach with maternal-fetal medicine specialists and skilled anesthesiologists, reinforcing the notion that in vitro fertilization should not be withheld as a treatment modality from patients with obesity.