Jianxi Jiang,* Xiaohan Wu,* Hongliang Sun, Lei Han, Xianghui Zhang, Chunjiao Liu, Yanlin Wang, Qingchun Li

Department of Reproductive Medicine, Binzhou Medical University Hospital, Binzhou, Shandong, 256603, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Qingchun Li, Department of Reproductive Medicine, Binzhou Medical University Hospital, Binzhou, Shandong, 256603, People’s Republic of China, Tel +05433258715, Email liqc1@126.com Yanlin Wang, Department of Reproductive Medicine, Binzhou Medical University Hospital, Binzhou, Shandong, 256603, People’s Republic of China, Tel +05433258713, Email docylwang2003@126.com

Objective: The aim of this study is to assess the impact of different embryo transfer strategies, focusing on cleavage-stage embryos and blastocysts, on pregnancy and neonatal outcomes in frozen-thawed embryo transfer (FET) cycles among women < 35 years old and ≥ 35 years old.
Methods: A retrospective cohort analysis of 3,065 FET cycles performed between April 2015 and October 2022 categorized patients into seven groups by embryo morphology, quality, and quantity: single/double high-quality cleavage (A/B), single/double high-quality blastocyst (C/D), single/double poor-quality blastocyst (E/F), and mixed-quality blastocyst (G). Stratified by age (< 35/≥ 35 years), outcomes (clinical pregnancy, live birth, multiple pregnancy, preterm birth) were analyzed using non-parametric tests and chi-square.
Results: In women < 35 years, transferring two high-quality cleavage embryos (Group B) yielded higher clinical pregnancy (60.12% vs 28.57%) and live birth rates (51.45% vs 19.64%) than single high-quality cleavage embryos (Group A; P < 0.05). For blastocyst transfer, double high-quality blastocysts (Group D) showed higher multiple pregnancy and preterm birth rates than single high-quality blastocysts (Group C; P < 0.05). In women ≥ 35 years, Group B had superior pregnancy outcomes compared to Group A, while Group D demonstrated significantly higher clinical pregnancy and live birth rates than Group C (P < 0.05). Transferring two poor-quality blastocysts (Group F) improved live birth rates in older patients compared to single poor-quality blastocysts (Group E; 31.91% vs 14.29%, P < 0.05). No significant differences in neonatal birth weight were observed across age groups.
Conclusion: For FET cycles, transferring two high-quality cleavage embryos is recommended for all ages. Women < 35 years should prioritize single high-quality blastocyst transfer to minimize multiple pregnancies and preterm births, while those ≥ 35 years benefit from double high-quality blastocysts. Transferring two poor-quality blastocysts may enhance pregnancy outcomes in older patients. These findings warrant validation through multicenter studies to ensure clinical applicability.

Keywords: blastocyst transfer, cleavage-stage embryos, frozen-thawed embryo transfer, FET, neonatal outcomes, pregnancy outcomes