COMPARABLE PREGNANCY OUTCOMES BETWEEN HIGH-SCORE BLASTOCYSTS WITH LOWER EXPANSION GRADE ON DAY 5 AND HIGHER EXPANSION GRADE ON DAY 6: AN ANALYSIS OF 1751 FROZEN-THAWED CYCLES

Abstract

To identify blastulation and expansion grade predictive of pregnancy and live births outcomes with high-score blastocysts in frozen-thawed transfer cycles. A retrospective study was conducted with clinic-based data in the Reproductive Medicine Centre of the Sixth Affiliated Hospital of Sun Yat-sen University from February 2014 to April 2020. High-score blastocysts frozen on day 5 (grade 3AA, 3AB, 3BA or 3BB) or day 6 (grade ≥4 and neither C grades in the evaluations of ICM nor TE) using vitrification-freezing protocol were included. Endometrial preparation was carried out with natural cycle, hormone replacement cycle or controlled ovarian hyperstimulation cycle accordingly. Progesterone administration was commenced when the thickness of endometrium reached 8 mm or more. Single embryo was transferred on day 5 after ovulation or progesterone supplementation. Difference in baseline characteristics, characteristics of embryo transfer cycles and clinical outcomes between two groups were assessed. Statistical analyses were performed stratified by age and anti-Müllerian hormone (AMH). A total of 617 blastocysts in day 5 group and 1134 blastocysts in day 6 group were assessed. As a whole, patients in day 5 group were younger than patients in day 6 group (34.22 versus 34.73, P = 0.041). No significant differences were observed in characteristics of transfer cycles, clinical pregnancy rate and live birth rate between groups. Stratified analyses showed that the biochemical pregnancy rate and clinical pregnancy rate were higher in day 5 group for patients aged below 30 years (60.6% versus 43.8%, P = 0.001 and 55.8% versus 38.2%, P < 0.001, respectively) when basic patient demographics were comparable, while rates of miscarriage, ongoing pregnancy and live birth were similar between groups. No significant differences were found in pregnancy outcomes for patients in other subgroups (31 to 35 years, 36 to 40 years, > 40 years). Stratified by AMH (< 1.1 ng/ml or ≥1.1 ng/ml), pregnancy outcomes were all comparable between day 5 group and day 6 group. In frozen-thawed transfer cycles, the pregnancy potential of high-score blastocysts with lower expansion grade on day 5 and higher expansion grade on day 6 are comparable for patients aged above 30 years.