The effect of fresh vs. frozen embryo transfer on neonatal and pediatric weight and weight gain trajectory

Previous studies have identified a relationship between frozen embryo transfer and large for gestational age infants, which may be hypothesized to have an effect on childhood obesity and long-term health outcomes. This study aimed to evaluate the effect of frozen, compared to fresh, embryo transfer on neonatal and pediatric weight and weight gain trajectory. This retrospective cohort study evaluated women who underwent fresh and/or frozen embryo transfer at Mayo Clinic, Rochester from 2010 to 2014. All embryo transfers included in this study resulted in a singleton live birth. Children were followed from birth to at least 18 months to evaluate weight and growth trajectory. When possible, growth was evaluated to 5 years of age. Baseline maternal characteristics, embryo transfer data, pregnancy data, and neonatal and pediatric growth parameters were collected by chart review. Age and sex specific group percentiles were calculated using the WHO child growth standards. Propensity score methodology using inverse probability weighting (IPW) was used to balance the two groups (fresh vs. frozen embryo transfer) on maternal characteristics (age at delivery, race, baseline body mass index, parity, gravidity, and pregnancy weight gain, and pregnancy complications) and gestational age before evaluating outcomes. Each infant growth measurement was compared between the two groups using weighted general linear model. Of the 136 women, 87 underwent a fresh embryo while 49 underwent a frozen embryo transfer. Birth length and head circumference were significantly different in infants delivered after fresh vs. frozen embryo transfer, however the difference in birth weight was not statistically different (Table 1). Long term growth measurements including age- and sex-specific weight, height, and BMI percentiles were not significantly different between groups (Table 1). This study found no effect of fresh vs. frozen embryo transfer on neonatal weight and childhood weight gain trajectory. There was a statistically significant difference in birth length and head circumference in infants delivered after fresh vs. frozen embryo transfer. These differences do not seem to be clinically significant.