The effect of maternal body mass index on embryo division timings in women undergoing in vitro fertilization

OBJECTIVE: To measure the impact of maternal body mass index (BMI) on the morphokinetics of embryo development as monitored by a time-lapse system. DESIGN: A retrospective chart review of in vitro fertilization (IVF) cycles from September 2016 to January 2019. SETTING: Academic IVF practice. PATIENT(S): Patients <age 38 years undergoing IVF with their own gametes. INTERVENTION(S): Not applicable. MAIN OUTCOME MEASURE(S): The primary outcome was to compare embryo division timings between morbidly obese, obese, overweight, and normal-weight patients. A multilevel mixed effects model was performed to investigate the relationships between BMI categories and embryo division timings. Log or square transformation were used to improve fit. RESULT(S): A total of 366 patients met inclusion criteria, yielding 4,475 embryos: 1,948 embryos from 162 normal-weight women (BMI 18.5–24.9), 1,242 embryos from 96 overweight women (BMI 25.0–29.9), 1,119 embryos from 91 obese women (BMI 30.0–39.9), and 166 embryos from 17 morbidly obese women (BMI ≥40). There were no differences in age, Antimüllerian hormone, or IVF cycle outcomes among the different BMI categories. When comparing embryo division timings based on BMI, controlling for covariates, embryos from obese patients had a shorter time to division to 2 cell embryo (T2) than normal-weight patients. When analyzing BMI as a continuous variable, there was no significant relationship between BMI and embryo division timing. CONCLUSION(S): Early embryo divisions were accelerated in only certain categories of obesity. This suggests a more complex mechanism for the effect of obesity on embryo development that may not be perceptible through the assessment of cell division timing events.