LASER ASSISTED HATCHING FOR HUMAN CRYOPRESERVED CLEAVED EMBRYOS

The objectives of this study were to evaluate the impact of two different sizes of zona pellucida thinning area by laser assisted hatching on the clinical outcome of cryopreserved cleaved embryos (Experiment 1) and two different sizes of zona pellucida opening area by laser assisted hatching on the clinical outcome of cryopreserved cleaved embryos that were cultured to blastocyst (Experiment 2). A total of 120 cryopreserved cleaved embryo transfers were assigned to either quarter or half of zona pellucida thinning group. Laser assisted hatching was conducted at the cleavage-stage. The rates of clinical pregnancy (47 versus 25%) and implantation (32 versus 16%) were significantly greater in the half thinning group than in the quarter thinning group (P = 0.0218 and P = 0.0090, respectively) (Experiment 1). A total of 71 cryopreserved cleaved embryo transfers were assigned to either one eighth or half of zona pellucida opening group. The cryopreserved cleaved embryos were cultured to blastocyst and laser assisted hatching was conducted at the blastocyst-stage. The rates of clinical pregnancy (74 versus 43%) and implantation (52 versus 27%) were significantly greater in the half opening group than in the one eighth opening group (P = 0.0090 and P = 0.0117, respectively) (Experiment 2). Our results suggest that the size of zona pellucida thinning area or opening area can affect the clinical outcome of cryopreserved cleaved embryo transfers.