Comparison of zona manipulated and zona intact blastocyst transfers: a prospective randomized trial

In this prospective randomized study the effects of enzymatic treatment of zona pellucida of blastocysts on implantation and pregnancy rates were evaluated in a group of patients who had more than five embryos on day 3.

Forty-six patients with a mean age of 29.8 +/- 4.5 years and mean duration of infertility of 6.72 +/- 0.63 years had blastocyst stage transfers, with a mean number of 2.9 +/- 0.1 embryos replaced per patient. Patients were randomly divided into two groups. The first group consisted of patients (n = 22) who had zona intact blastocyst stage transfers and the second group consisted of patients (n = 24) who had zona manipulated (enzymatic treatment) blastocyst stage transfers. Patient and cycle characteristics were similar in both groups. A commercial cell and serum-free sequential culture system was used for all embryos.

Overall blastocyst formation rate was 50.3%. Transfer could be done in all patients. The positive beta-human chorionic gonadotropin rate in the zona intact group was 50% (11/22) and in the zona-manipulated group was 70.8% (17/24). Clinical pregnancy, ongoing pregnancy, and implantation rates in zona intact and manipulated groups were 45.5%, 27.3%, and 19%, and 62.5%, 45.8%, and 24% respectively. Although implantation and pregnancy rates in the zona-manipulated group were higher, there were no statistically significant differences in terms of these variables between two groups. No triplet pregnancy was obtained in either group, and the twin pregnancy rate was 20% (2/10) in the zona intact group and 13.3% (2/15) in the zona-manipulated group.

With further improvements in the embryo culture systems it will become possible in the near future to achieve high implantation rates even with single blastocyst transfers. Enzymatic treatment of the zona pellucida seems that it does not alter the pregnancy and implantation rates, but further studies with larger group of patients are needed to clarify the real effect of this zona manipulation on pregnancy outcome.