Blastocyst transfer after enzymatic treatment of the zona pellucida: improving in-vitro fertilization and understanding implantation

It has been shown recently that delayed transfers improve implantation rate s in assisted reproductive technology programmes. In a prospective study, t he pregnancy rates and safety of outcome were evaluated in a group of patie nts after the transfer of day 5 blastocysts with enzymatic treatment of the zona pellucida. Nineteen women with a mean age of 32.6 +/- 5.2 years and m ean 2.1 +/- 2.2 repeated attempts had blastocyst transfers with a mean numb er of 2.5 +/- 0.7 embryos replaced per patient. The clinical pregnancy rate s per cycle/transfer and implantation rate were 53% and 33%, respectively. The multiple pregnancy rate was 40% (two pregnancies were triplets). The pr egnancy and implantation rates mere very much higher than observed for most assisted reproduction technology centres, The 'in-vitro implantation" rate s of zona-free blastocysts on a variety of feeder monolayers was 92%, offer ing some thoughts as to the role of the zona and interaction of the inner c ell mass and trophoectoderm with the endometrium in implantation, Based on the in-vitro studies and the high multiple pregnancy rates, it appears that zona-manipulated blastocysts implant relatively well and there would be a need to reduce the number of transferred embryos to one or two, thus reduci ng multiple pregnancies and having spare blastocysts available for cryopres ervation, The results also suggest that using the embryo culture protocol a nd method of transfer in the present study offers encouraging improvements to assisted reproduction technology, and enzymatic treatment of the zona ma y allow better anchorage and dialogue of the embryo with the endometrium, h elping us to improve and understand implantation.