Implantation enhancement by selective assisted hatching using zona drilling of human embryos with poor prognosis

Abstract

Assisted hatching by zona drilling using acidic Tyrode's solution was performed during three randomized trials in 330 in-vitro fertilization patients. The trials were designed in order to study the overall effect of the procedure and whether characteristic patient [i.e. maternal age and basal levels of follicle stimulating hormone (FSH)] and embryonic features (i.e. zona pellucida thickness) are important for the decision to perform assisted hatching routinely. Couples (n = 137; Trial 1) in whom the female partner had normal basal FSH levels were randomized in a control group (without micro-manipulation) and a zona drilling group (all embryos micro-manipulated). The incidence of implantation (67/239; 28%) of zona-drilled embryos compared favourably with that of control embryos (49/229; 21%), but the difference was not significant. Retrospective analysis revealed that those embryos whose zonae were thicker than 15 μon were rescued. In order to test the validity of this finding, selective assisted hatching was performed on embryos with a poor prognosis in 163 other patients (Trial 2). The couples were randomized into a control group and a group in which embryos were selectively zona-drilled, based on zona thickness and other embryonic features. The rate of embryonic implantation in the selectively zona-drilled group was 25% (70/278), significantly (P < 0.05) higher than that of control embryos (51/285; 18%). Although it was demonstrated retrospectively and prospectively that assisted hatching by zona drilling is effective in embryos with thick zonae (≧$15 μm), patients whose embryos have thin (<13 μm) zonae may be jeopardized by the procedure. Selective assisted hatching appeared most effective in women over 38 and in those with elevated basal FSH levels.