pArtiaL zonA pelluciDa Removal by assisteD hatchINg of Blastocysts

Zona pellucida (ZP) manipulation, termed "assisted hatching" (AH), has been introduced in order to favor embryo hatching and ultimately improve assisted reproductive technology success but with poor proofs of safety and biological plausibility.

Vitrifying and warming of blastocysts may impair the successful hatching process of the embryo out of its ZP and its following implantation into the uterus. Theoretically, AH may facilitate the hatching process and subsequently increase implantation rates.

In this prospective randomized controlled trial (RCT), the hypothesis is to test whether the application of a partial AH to vitrified/warmed blastocysts might affect patients' delivery rate.

Patients with vitrified blastocysts will be randomized at the time of blastocyst warming to a study group (with AH) or a control group (without AH). AH will be performed at the expanded blastocyst stage using a laser technique and a laser opening will be initiated at the 1 o'clock position. Consecutive laser shots will be applied to reach the 5 o'clock position of the blastocyst. The blastocysts will then be cultured at least 2 h and subsequently transferred into the patient's uterus.

Inclusion criteria

• single embryo transfer of vitrified/warmed blastocyst (SET)
• first or second frozen IVF (with or without Intracytoplasmic Sperm Injection) cycle of blastocysts
• first or second oocyte retrieval

Exclusion criteria

• Preimplantation Genetic Testing (PGT) cycle
• BMI > 35 kg/m2
• severe male factor
• abnormal uterine cavity