A prospective, randomized, double-blinded study of assisted hatching in women younger than 38 years undergoing in vitro fertilization

Objective: To determine whether assisted hatching is beneficial to IVF patients younger than 38 years whose embryos have a thickened zona pellucida (ZP). Design: Prospective, randomized, double-blinded, crossover study. Setting: University-based infertility center. Patient(s): One hundred twenty-one women less than 38 years of age, undergoing IVF at Washington University between April 2004 and February 2007, with ZP thickness ≥13 μm for any embryos. Intervention(s): Measurement of ZP thickness in embryos undergoing IVF; randomization of women with embryos with ZP thickness ≥13 μm to no procedure or assisted hatching performed by acidic Tyrode's solution. Main Outcome Measure(s): Clinical intrauterine pregnancy rate, implantation rate, spontaneous pregnancy loss, and live birth rate. Result(s): Baseline characteristics and ZP thickness were not significantly different between the two study arms (hatched and unhatched). No significant differences were observed between hatched and unhatched patients in the rates of clinical pregnancy (47% vs. 50% respectively) or live birth (46% vs. 45% respectively). Further, no significant differences were noted between hatched and unhatched groups in rates of spontaneous abortions, monozygotic twinning, dizygotic twinning, chromosomal abnormalities, or ectopic gestations. In addition, mean ZP thickness did not have a significant effect on pregnancy. Conclusion(s): In patients younger than 38 years with embryos with ZP thickness of ≥13 μm, assisted hatching does not improve the rates of implantation, clinical pregnancy, or live birth, and thus does not appear to offer any benefit to patients in this age group undergoing IVF.