Zona pellucida removal and vitrified blastocyst transfer outcome: a preliminary study.

The objective of this study was to investigate whether a change in assisted hatching technique from partial opening to total removal of the zona pellucida improved the outcome of vitrified blastocyst transfer. This was a preliminary observational study conducted from November 2003 to April 2006. Partial opening using acid Tyrode's solution was performed in 45 cycles, while total removal using a laser and mechanical pipetting was performed in 57 cycles. The clinical pregnancy, implantation, and delivery rates were higher in the total removal group than in the partial opening group (67% versus 42%, P < 0.02; 55% versus 30%, P < 0.01; 56% versus 36%, P < 0.04, respectively). These results suggest that total removal of the zona pellucida is associated with higher pregnancy, implantation and delivery rates compared with partial opening for vitrified blastocyst transfer.