Obstetric outcomes after transfer of vitrified blastocysts

It has been claimed that the risks to the child resulting from vitrification as compared with the slow-freezing technique, may be higher owing to the high concentrations of potentially toxic cryoprotectants. We therefore retrospectively compared the obstetric and neonatal outcomes in a cohort of children born after transfer of vitrified blastocysts, fresh blastocysts and slow-frozen early cleavage stage embryos.

All children born after transfer of vitrified blastocysts (n = 106), fresh blastocysts (n = 207) and slow-frozen early cleavage stage embryos (n = 206) during the period January 2006 to May 2008 at Fertility Center Scandinavia were included. Data on obstetric and neonatal outcomes were obtained from medical records from the antenatal and delivery clinics.

For singletons, there were no significant differences between the groups in gestational age, mortality or birth defects. After adjustment for parity and BMI, birthweight was significantly higher in singletons born after transfer of vitrified blastocysts as compared with after transfer of fresh blastocysts (median 3560 versus 3510 g, P = 0.0311). More singletons born after transfer of fresh blastocysts were small for gestational age compared with singletons born after transfer of vitrified blastocysts (12.1 versus 3.0%, P = 0.0085). A higher rate of major post-partum haemorrhage was observed in the vitrified blastocyst group as compared with the other two groups (25.0 versus 6.0 and 7.5%).

No adverse neonatal outcomes were observed in children born after transfer of vitrified, as compared with fresh blastocysts or after transfer of slow-frozen early cleavage stage embryos.