O-201 Growth of singletons born after frozen embryo transfer until early adulthood: a Finnish register study

Abstract Study question Does the growth of children born after frozen embryo transfer (FET) differ from those born after fresh embryo transfer (ET) or natural conception (NC)? Summary answer Boys born after FET have a higher risk of overweight compared to fresh ET. What is known already FET is associated with a higher mean birth weight and an increased risk of large-for-gestational-age (LGA) compared to fresh ET and NC, thus raising questions of possible growth disturbances later in life. Previous studies on early childhood growth after FET have reported partly contradictory results. Moreover, data on the adolescent growth after FET are scarce, reporting no significant differences. Study design, size, duration This observational cohort study, based on national population-based registers, includes 1825 and 2933 singletons born after FET and fresh ET in Oulu and Helsinki city areas in Finland between 1995 and 2006. A 10% sample of NC controls (n = 31 136) from the same birth years, matched for area of residence, was obtained from the Finnish Medical Birth Register. Growth data were obtained from the Register of Primary Health Care visits. Participants/materials, setting, methods Mean heights, weights, and body mass indices (BMI) were compared between the groups, stratified by sex, between ages 7 and 18, using general linear model. The proportions of overweight (age- and sex-adjusted ISO-BMI for children ≥ 25) were analyzed using multiple linear regression, adjusting for birth year, preterm birth, maternal age, parity, and socioeconomic status. Additionally, the odds for overweight were calculated for all ages combined, adjusting for multiple measurements using generalized estimating equations. Main results and the role of chance Growth measurements for each age were available for 5.9-30.6% of boys and 4.7-29.5% of girls. The mean and median number of measurements was three per child. No significant differences in height were found between FET and fresh ET. FET boys were significantly taller compared to NC between ages 11 and 14. For boys, the mean proportions of overweight for FET, fresh ET and NC were 28%, 22% and 26%, respectively (p