Outcomes of human blastocyst transfer after slow-freezing using sequential culture: a clinical report

To present our experience using slow-freezing from 2005 to 2008, with subsequent newborn outcomes after transfer of thawed blastocysts.

There were 148 cycles programmed for frozen blastocyst transfer, which resulted in 142 embryo transfers. Blastocysts were cultured in sequential media, and programmed slow-freezing was performed in an apparatus using a modified Ménézo and Veiga method. Thawing occurred at room temperature under a stream of 5% CO(2), and embryos were transferred about 2 h after thawing.

Seventy percent of the blastocysts survived. The clinical pregnancy rate was 43%, the implantation rate was 27.7% and the rate of live birth was 38%. Twin gestations occurred in 19.7% of clinical pregnancies, the newborn twin rate was 6.5% per clinical pregnancy, the male to female ratio was 1.04, and abortions occurred in 14.8% of clinical pregnancies. There was one newborn with a 47, XXY karyotype and another who developed a benign knee tumour.

The present results further support that extended culture to the blastocyst stage and an efficient freeze-thaw procedure for blastocysts are associated with high success rates.