Blastocoele re-expansion immediately after warming is a strong hallmark for predicting pregnancy outcome in single...

To investigate the correlation between blastocoele re-expansion immediately after warming and pregnancy outcomes in vitrified-warmed blastocyst transfer cycles in assisted reproductive technology.

A retrospective analysis was performed on 742 qualifying single vitrified-warmed blastocyst transfer cycles between January 2022 and December 2023 conducted at a single reproductive center. Blastocysts were imaged at immediately (designated 0 h) and 2 h after warming and were divided into two groups: group A (with blastocoele re-expansion at 0 h) and group B (without blastocoele re-expansion at 0 h). Blastocysts without blastocoele re-expansion at 2 h-indicating unsuccessful recovery-were excluded. Pregnancy outcomes following blastocyst transfer were then analyzed.

Among 742 cycles, 348 and 394 cycles were categorized as group A and group B, respectively. No significant differences in the patient's baseline characteristics were observed. The clinical pregnancy and live birth rates in group A (69.83% and 55.75%, respectively) were significantly higher than those in group B (54.82% and 45.43%, respectively). Logistic regression analysis showed that immediate blastocoele re-expansion was significantly correlated with clinical pregnancy and live birth. Moreover, the male birth rate in group A (1.59) was also significantly higher than that in group B (1.01). However, the miscarriage rate, monozygotic twinning and birth defects did not differ between the two groups.

Transfer of blastocysts showing blastocoele re-expansion immediately after warming is associated with high clinical pregnancy, live birth and male birth rates. This suggests that early re-expansion is a strong indicator for predicting pregnancy outcomes in vitrified-warmed blastocyst transfer cycles.