IMPACT OF ASSISTED HATCHING ON PREGNANCY
RATES IN WOMEN OF ADVANCED MATERNAL AGE

Authors: Wendy Chang, MD, Alan DeCherney, MD, Mark Surrey, MD, David Hill, PhD

Background and Significance: Despite significant advances in stimulation protocols and embryo culture techniques, pregnancy rates from in vitro fertilization-embryo transfer (IVF-ET) cycles remain low. This inefficiency has been ascribed to low implantation rates (<20%) resulting from poor embryo quality (>25% embryo volume composed of anucleate cell fragments), suboptimal endometrial receptivity, or both. Cultured embryos divide slowly in vitro, many failing to hatch and implant. Hardening of the zona pellucida as a consequence to in vitro culturing conditions has been implicated in decreased hatching rates. Also, zona thickness is directly correlated with age and FSH levels, and is negatively correlated with implantation rates.

Assisted hatching (AH) consists of various mechanical and chemical methods to focally disrupt the zona pellucida. Evidence suggests that hatched preimplantation embryos may implant a day sooner than unhatched ones. AH has therefore been proposed as a means to facilitate implantation in older women, who tend to have increased zona thickness.

Objective:: We wished to determine the impact of assisted hatching on pregnancy rates in women of advanced prematernal age (>35 years) undergoing their first IVF-ET cycle at our institution.

Materials and Methods:: We conducted a retrospective review of IVF-ET cycles from January 2002 to the present. Data were extracted from the laboratory records of all non-donor cycles in which the women were aged 35 years or greater. Pregnancy rates were determined for both groups based on positive serum chorionic gonadotropin levels (hCG) 14 days post embryo transfer. Data were analyzed using the student’s t-test and χ2 analysis as indicated.

Results:: A total of 2,374 embryos from 801 patients were included in our analysis (Table 1). Of these, 471 patients had assisted hatching performed on 1600 embryos. When hatching was performed, all embryos transferred were hatched. There was no significant difference between the +AH and –AH groups with respect to mean maternal age. However, the women in the +AH group tended to be older, with a greater number of women >40 years old. There was no significant difference in pregnancy rates (Figure 1) between the two groups, despite a higher number of embryos transferred in the +AH group.

Conclusion: Our data suggest that assisted hatching does not improve pregnancy rates in women >35 years of age undergoing their first IVF-ET. However, our retrospective review is limited by potential selection bias, as clinicians may tend to select those patients who are older, or poorer embryo grades for assisted hatching. Nevertheless, our data would not support the routine application of assisted hatching in all women >35 years.