Improved implantation rate after chemical removal of the zona pellucida.

ABSTRACT

OBJECTIVE: To evaluate the implantation rate achieved after chemical removal of the zona pellucida from day 5 human in vitro-derived embryos. DESIGN: Prospective, randomized, controlled study. SETTING: A tertiary care infertility clinic. PATIENT(S) Two hundred fifty-seven patients undergoing IVF with transfer of morulas or blastocysts on day 5 after oocyte retrieval. All patients had had at least two previous implantation failures. INTERVENTION(S) Chemical removal of zona pellucida by using acidic Tyrode's solution vs. no removal (controls). MAIN OUTCOME MEASURES: Clinical pregnancy rate and implantation rate per transfer. RESULT(S) Embryos without zona pellucida implanted at nearly twice the rate of control embryos (15.7% vs. 27.5%). The pregnancy rate was also significantly higher in the zona pellucida-free group than the control group (31.0% vs. 46.1%). Removal of zona pellucida was most effective in embryos with delayed development, which reached the morula or early cavitating stage on day 5 of in vitro culture (implantation rate, 12.1% vs. 25.7%). CONCLUSION(S) Chemical removal of zona pellucida from day 5 in vitro cultured human embryos is an effective and safe method of significantly improving the implantation rate, especially of embryos with delayed development.