Effect of the Interaction Between Pre-pregnancy Body Mass Index and Fresh/Frozen Embryo Transfer on Perinatal Outcomes of Assisted Reproductive Technology-Conceived Singletons: A Retrospective Cohort Study

Objective: To demonstrate the association between pre-pregnancy maternal overweight, obesity, and perinatal outcomes of singletons conceived by assisted reproductive technology (ART). Design: Retrospective cohort study from 2006 to 2015 data from a single ART center. Setting: Assisted Reproduction Center, Northwest Women's and Children's Hospital, Xi'an, Northwestern China. Patients: We included 7,818 women undergoing ART and their singleton infants. Interventions: None. Main Outcome Measure: The primary outcome measures were preterm birth (PTB), macrosomia, low birth weight, small for gestational age, and large for gestational age (LGA). Results: We experienced an increase in the risk of PTB, macrosomia, and LGA in overweight and obese groups compared with that in normal-weight groups [PTB: overweight vs. normal weight: odds ratio [OR] = 1.44, 95% CI: 1.18-1.75; obesity vs. normal weight: OR = 1.53, 95% CI: 1.04-2.25; macrosomia: overweight vs. normal weight: OR = 1.78, 95% CI: 1.48-2.14; obesity vs. normal weight: OR = 2.16, 95% CI: 1.52-3.06; LGA: overweight vs. normal weight: OR = 1.63, 95% CI: 1.39-1.90; obesity vs. normal weight: OR = 2.11, 95% CI: 1.57-2.83]. We observed a significant interaction between maternal BMI and fresh/frozen embryo transfer on PTB and LGA (P = 0.030; P = 0.030). Fresh embryo transfer significantly increased the effect of maternal BMI on LGA (fresh: OR = 1.14, 95% CI: 1.10-1.18; frozen: OR = 1.09, 95% CI: 1.04-1.13), and frozen embryo transfer increased the effect of maternal BMI on PTB (fresh: OR = 1.03, 95% CI: 0.99-1.08; frozen: OR = 1.09, 95% CI: 1.04-1.15). Conclusions: Pre-pregnancy maternal overweight and obesity were associated with higher risks of PTB, macrosomia, and LGA in ART-conceived singletons. These associations were affected by the timing of embryo transfer (fresh/frozen embryo transfer). Therefore, we recommend women before ART to maintain a normal BMI for the prevention of adverse perinatal outcomes.