The effect of vitrified–warmed blastocyst transfer on postnatal growth: a 1-year follow-up questionnaire study.

Is postnatal growth of singletons aged 12 months born after vitrified–warmed blastocyst transfer (frozen embryo transfer [FET]) different from children born after fresh blastocyst transfer? A retrospective cohort study conducted at a single university-affiliated obstetrics and fertility centre between 2014 and 2016. Women who underwent fresh transfer or FET at blastocyst stage and obtained a singleton live birth were included. Propensity score inverse probability weighting was used to balance baseline maternal characteristics between fresh and FET cycles. Of the 382 women with singleton live births, 124 underwent a fresh blastocyst transfer and 258 underwent a FET. Significantly higher birth weight and length z-scores were observed after FET (P = 0.01 and P = 0.002, respectively) compared with the fresh transfer group. At 12 months of age, the fresh and FET groups showed no significant effect on the weight z-score, but the FET was associated with a higher height z-score (P = 0.001) compared with fresh blastocyst transfer. The comparison between males and females from the same study group showed higher birth weight z-score for males in the FET group (P < 0.001). During the first 12 months, however, males in the FET group showed a slower growth trajectory in terms of weight (P = 0.007). At 12 months of postnatal life, an increased height and sex-dependent differences in growth trajectories were observed in singletons born after FET compared with those born after fresh embryo transfer. [ABSTRACT FROM AUTHOR]