Impact of embryo vitrification on children’s health, including growth up to two years of age, in comparison with results following a fresh embryo transfer

To assess health outcomes, including growth up to 2 years of age, in children born after embryo vitrification in comparison with children born after fresh embryo transfer.A prospective cohort study.A single-center university hospital.Singletons born after the transfer of vitrified or fresh embryos, either at the cleavage or blastocyst stage between 2014 and 2018, were included.Multiple linear and logistic regression analyses were used to study the association between outcomes after vitrified versus fresh embryo transfer, controlling for neonatal, treatment, and maternal characteristics. Subgroup analysis according to cycle protocol (hormone replacement vs. natural cycle) and strategy (freeze-all vs. previous fresh cycle) was also performed.Measurements at birth and growth in infancy and childhood, as well as health outcomes, including congenital malformations, interventions, medication use, and hospitalizations are reported.Birth characteristics were available for 1237 and 2063 children born after embryo vitrification and fresh embryo transfer, respectively. Follow-up data were available for 582 and 757 children at infancy and for 233 and 296 children at 2 years, respectively. Birthweight, height, and head circumference SD scores of children born after embryo vitrification were higher than children born after fresh embryo transfer, even after adjustment for neonatal, treatment, and maternal characteristics. In infancy, weight and height SD scores were larger for children born after embryo vitrification, but not after adjustment for covariates. In childhood, no differences in anthropometry were observed between the groups. Weight and height gain from birth to infancy and from infancy to early childhood were comparable between the groups. Comparable rates of severe developmental problems, hospital admissions, surgical interventions, and of chronic medication use were observed up to the age of 2 years. Subgroup analysis showed that growth parameters were not affected by the cycle protocol or strategy at any age.Our study indicated that embryo vitrification is associated with higher birthweight, even after controlling for confounders. However, in early childhood, anthropometry and weight and height gain was not different in children born after vitrified or fresh embryo transfer.