OBJECTIVE: To examine whether opening of the zona pellucida (i.e., assisted hatching) accelerates implantation. DESIGN: In a controlled, randomized trial, patients were assigned to control and assisted hatching groups. SETTING: All patients studied were of the Center for Reproductive Medicine at Cornell University Medical College. INTERVENTION: All patients underwent stimulation with gonadotropins after luteal phase GnRH down regulation. Assisted hatching with zona drilling using acidic Tyrode's solution was performed on the assigned embryos. MAIN OUTCOME MEASURES: Luteal E2, P, and hCG on days +5, +6, +7, +8, +9, +11, +13, and +15 were measured. The implantation time, peak midluteal E2 and intervals between these two values were studied. RESULTS: Implantation occurred significantly earlier in the assisted hatching group. The interval between implantation and peak midluteal E2 was also significantly shorter in the assisted hatching group than in the controls. However, there was no significant difference in the day of the peak midluteal E2 between the assisted hatching and control groups. CONCLUSION: Assisted hatching may enhance embryo implantation not only by mechanically facilitating the hatching process but also by allowing earlier embryo-endometrium contact. Such early contact may enhance embryonic development potential and may optimize synchronization between embryo and endometrium, resulting in improved implantation efficiency.
