The Risk of Birth Defects Among Children Born After Vitrified Blastocyst Transfers and Those Born After Fresh and Vitrified Cleavage-stage Embryo Transfers

Purpose: To explore the risk of birth defects among children born after vitrified blastocyst transfers and those born after fresh and vitrified cleavage-stage embryo transfers.

Methods: A retrospective cohort study was conducted including infants born after fresh and vitrified day 3 embryo transfers and those born after vitrified day 5 or 6 blastocyst transfers from January 2005 through December 2016. The outcome measures included any birth defect, multiple birth defects and 13 individual categories of birth defects.

Results: Any birth defect occurred in 1.15% of infants born after fresh day 3 embryo transfers, 1.75% of infants born after vitrified day 3 embryo transfers, 1.60% of infants born after vitrified day 5 blastocyst transfers and 1.10% of infants born after vitrified day 6 blastocyst transfers. There was no difference in the risk of birth defects between vitrified blastocyst-stage transfers and vitrified cleavage-stage transfers (including day 5 vs. day 3 and day 6 vs. day 3) among all births or in only singletons or twins. For infants born after cleavage-stage embryo transfers at day 3, there was no difference in the risk of birth defects between fresh embryo transfers and vitrified embryo transfers among all births or in only singletons or twins.

Conclusions: Transfer of vitrified day 5 or 6 blastocysts does not increase the risk of birth defects compared with vitrified day 3 embryos. However, randomized control trials and follow-up studies of the long-term outcome of children born after blastocyst-stage transfers are needed to confirm the clinical safety of extending embryo culture to the blastocyst stage.