A shorter pre-vitrification equilibration time for laser-collapsed human blastocysts is associated with a lower...

Frozen embryo transfer in humans, especially at the blastocyst stage, provides a valid alternative to fresh embryo transfer. However, protocols for blastocyst vitrification are 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. This study compared the clinical and neonatal outcomes involving vitrified-warmed blastocysts.

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 of human blastocysts.