No advantage of single day 6 good-quality blastocyst transfer versus single day 5 poor-quality blastocyst transfer in frozen-thawed cycles stratified by age: A retrospective study

Abstract Background Blastocyst developmental speed, morphological grading and patient age are associated with pregnancy outcomes of frozen-thawed cycles. This study aimed to compare the clinical and neonatal outcomes between poor-quality D5 blastocysts and good-quality D6 blastocysts, and to investigate the transfer strategy for D6 blastocysts based on morphological grading and patient age. Methods A total of 3,486 cycles were divided into four groups: group A (n = 723) received one D5 poor-quality blastocyst; group B (n = 900) received one D6 good-quality blastocyst; group C (n = 619) received one good- and one poor-quality D6 blastocysts; and group D (n = 1244) received two good-quality D6 blastocysts. Pregnancy and neonatal outcomes were compared among the four groups stratified by 35 years of age. Results Live birth rate of D5 poor-quality blastocysts was higher than that of D6 high-quality blastocysts for patients aged < 35 years (35.48% vs. 31.13%, p  > 0.05), but there was no statistical difference. The same trend was showed for patients aged ≥ 35 years (29.09% vs. 21.28%, p  > 0.05). When patients were in the same age group, the live birth rate and multiple pregnancy rate in group B were significantly lower than those in groups C and D. The multiple pregnancy rate of double D6 blastocyst transfer is over 20%. Additionally, the birth weight of groups C and D was significantly lower than that of group B, and the trend disappeared if the patients were sub-grouped by singleton or twin birth. In total, for patients transferred with double D6 blastocysts, approximately 70% of preterm births and approximately 86% of low birth weight babies resulted from multiple pregnancies. Conclusions The preferential selection of poor-quality D5 blastocysts for transfer compared to high-quality D6 blastocysts is recommended, especially for advanced age patients. Single good-quality D6 blastocyst transfer can be considered for patients aged < 35 years. Additionally, adding a poor-quality D6 blastocyst, that is, double D6 blastocyst transfer, was suggested for patients ≥ 35 years of age to improve the live birth rate, but patients should be informed that this comes at the cost of increased risk of multiple pregnancies. However, double good-quality D6 blastocyst transfer is not recommended, regardless of age.