D6 high-quality expanded blastocysts and D5 expanded blastocysts have similar pregnancy and perinatal outcomes following single frozen blastocyst transfer

Objective

We compared the pregnancy and perinatal outcomes between expanded blastocysts vitrified on D5 versus D6 following single frozen blastocyst transfer.

Methods

Clinical data on 7,606 cycles of frozen-thawed blastocyst implantations were retrospectively analyzed. Depending on whether blastocysts were vitrified on D5 or D6 and the transferred blastocysts, the blastocysts were divided into 6 groups: HQB-D5, HQB-D6, 4XC-D5, 4XC-D6, 4CX-D5, and 4CX-D6 groups. The differences in clinical pregnancy rate, live birth rate, first trimester abortion rate, preterm birth rate, gestational age, birth weight, and sex ratio at birth among the groups were compared.

Results

Our study showed that there was no difference in pregnancy and perinatal outcomes between the delayed formation of D6 high-quality expanded blastocysts and D5 expanded blastocysts, whether they were high-quality blastocysts or not. For low-quality blastocysts, the clinical pregnancy rate of D5 was higher than that of D6, and D5 was also better than D6 in live birth rate for those with inner cell mass rating B or above, while there was no difference between D5 and D6 for those with inner cell mass rating C.

Conclusion

Based on our research, we suggest that when we are developing the implantation strategy, we give priority to the selection of high-quality expanded blastocysts, regardless of D5 and D6, whose clinical outcomes are not different. For low-quality blastocysts, D5 expanded blastocysts are preferred for transfer.

Artificial blastocoel collapse of human blastocysts before vitrification and its effect on re-expansion after warming - a prospective observational study using time-lapse microscopy

Vitrified human blastocysts show varied re-expansion capacity after warming. This prospective observational study compared behaviour of artificially collapsed blastocysts (study group patients, n = 69) to that of blastocysts that were vitrified without artificial collapse (control group patients, n = 72). Warmed blastocysts were monitored by time-lapse microscopy and blastocoel re-expansion speed and growth patterns compared between study and control groups. These parameters were also retrospectively compared between blastocysts that resulted in live birth and those that failed. Artificially collapsed blastocysts re-expanded on average 15.01 µm²/min faster than control blastocysts (P = 0.0013). Warmed blastocysts expressed four different patterns of blastocoel growth. The pattern showing contractions at the end of culture was observed to have a lower prevalence in control blastocysts, which coincided with the lower incidence of hatching in this group. Re-expansion speed and prevalence of growth patterns were comparable between blastocysts that did and did not result in a live birth. This was seen in the study and control groups. Despite faster re-expansion and different growth patterns of artificially collapsed blastocysts, live birth rate did not differ between groups. However, this result should be interpreted with caution due to the small sample size and high risk of bias.