Abstract

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.

MeSH

Blastocyst, Pregnancy, Birth Rate, Parturition, Pregnancy Outcome, Embryo Transfer, Premature Birth, Live Birth, Pregnancy, Multiple