Received December 10, 2024
Accepted June 02, 2025

In humans, frozen embryo transfer especially at the blastocyst stage provides a valid alternative to fresh embryo transfer. The protocols for blastocyst vitrification are however not yet standardized; for example, exposure to the first equilibration solution before vitrification commonly ranges from 2-3 minutes at 37�C or 2-15 minutes at room temperature. The main aim of this prospective study was to compare the clinical and neonatal outcomes for 831 warmed blastocysts, returned in 585 frozen embryo transfers with two exposure times to the equilibration solution at room temperature: (A) 7-8 minutes and (B) 9-10 minutes. The patients� characteristics were comparable between the two groups with no significant difference in their mean age, the average number of blastocysts transferred, basal Follicle Stimulating Hormone, body mass index (BMI), infertility duration, primary infertility, or endometrial thickness. The survival and clinical pregnancy rates of the vitrified-warmed laser collapsed blastocysts were not different between the two groups. The overall miscarriage rate was significantly lower in the 7-8 minute compared to the 9-10 minute equilibration group (A: 7.6% versus B: 14.2%, p < 0.05). Live birth, multiple gestation and neonatal outcomes were similar between the two groups. Our results indicate that the equilibration time can affect the efficiency of the cryopreservation process.