Assisted hatching by partial zona dissection of human pre-embryos in patients with recurrent implantation failure after in vitro fertilization

Objective: To examine the potential of the partial zona dissection technique to promote successful implantation by assisting embryo hatching after IVF. Design: The study and the control group included 72 and 82 patients, respectively, each had undergone at least three failed IVF-ET attempts. Assisted hatching was performed on four- to six-cell stage embryos by creating a slit in the zona pellucida using the partial zona dissection technique. After 90 minutes incubation (5% CO₂, 37°C), the embryos were transferred to the uterus. Setting: Infertility and IVF Unit of an academic tertiary referral medical center. Results: In the assisted hatching group, 230 micromanipulated embryos were replaced (3 or 4 treated embryos per patient) compared with 295 nonmanipulated embryos in the control group. Clinical pregnancy rates (PRs) were similar in the assisted hatching and control groups (n = 15; 20.8% and n = 12; 14.6%, respectively). However, the contribution of assisted hatching by partial zona dissection to successful implantation was related to the patients's age: patients older than 38 years showed a markedly higher PR after assisted hatching: 23.9% in the study group compared with only 7% of the controls. Conclusions: These results demonstrate that assisted hatching by partial zona dissection is a quick and efficient method that does not induce any visible damage to the embryos replaced. In a selected group of patients (aged over 38 years, who have failed to conceive in at least three previous IVF attempts) it significantly increases the chances for pregnancy after ET.