Mechanical zona pellucida removal of vitrified-warmed human blastocysts does not affect the clinical outcome

Abstract Research Question Does complete mechanical removal of the zona pellucida modify the outcome of transfer of vitrified-warmed human blastocysts? Design In a prospective randomized controlled study: a total of 419 couples were allocated to either zona pellucida-free (n=209) or zona intact (n=210) vitrified-warmed embryo transfer. Main outcome measures included clinical pregnancy, implantation and ongoing pregnancy rates. Results Transfer of zona pellucida-free blastocysts resulted in clinical pregnancy, implantation and ongoing pregnancy rates (35,9%, 33,9% and 32,1%, respectively) similar to those achieved with zona intact control embryos (39%, 36,4% and 33,1%, respectively). Conclusion Total mechanical removal of the zona pellucida did not affect the tested parameters of clinical outcomes.