# A shorter pre-vitrification equilibration time for laser-collapsed human blastocysts is associated with a lower miscarriage rate in ART treatments

## TL;DR

Shortening the equilibration time before freezing blastocysts may reduce miscarriage rates in assisted reproductive treatments.

## Contribution

This study shows that a shorter equilibration time (7-8 minutes) is linked to lower miscarriage rates in frozen embryo transfers.

## Key findings

- The miscarriage rate was significantly lower in the 7-8 minute equilibration group (7.6%) compared to the 9-10 minute group (14.2%).
- Clinical pregnancy and survival rates were similar between the two equilibration time groups.
- Live birth and neonatal outcomes were not significantly different between the groups.

## Abstract

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.