# Frozen-thawed double cleavage-stage or frozen-thawed single day 6 blastocyst stage embryo transfer: which is preferable for patients younger than 35 without day 5 blastocyst formation?

## TL;DR

The study compares embryo transfer strategies for young patients without day 5 blastocysts and finds that transferring a single good-quality day 6 blastocyst leads to better pregnancy outcomes.

## Contribution

The study identifies optimal embryo transfer strategies for freeze-all patients under 35 without day 5 blastocysts.

## Key findings

- Single good-quality day 6 blastocyst transfer had higher pregnancy and implantation rates than inferior-quality blastocysts or cleavage embryos.
- Double cleavage-stage embryos had higher live birth rates but also higher multiple pregnancy rates compared to single blastocyst transfers.
- Early miscarriage rates were significantly higher for inferior-quality day 6 blastocysts compared to other groups.

## Abstract

To compare the clinical outcomes between frozen-thawed cleavage embryo transfer and frozen-thawed day 6 blastocyst transfer in patients younger than 35 using the freeze-all strategy without day 5 blastocyst formation.

This was a retrospective observational analysis performed between January 2018 and December 2022 at the Reproductive and Genetic Specialist Hospital of the First Affiliated Hospital of Zhengzhou University. A total of 576 patients younger than 35 who used the “freeze-all strategy” but produced no day 5 blastocysts were recruited. The patients were divided into 3 groups according to the number and stage of the transferred embryos: double cleavage-stage embryos (Group A), single good-quality day 6 blastocysts (Group B) and single inferior-quality day 6 blastocysts (Group C),and several pregnancy outcomes were measured.

Groups A and B exhibited significantly higher chemical (73.7%, 67.0% versus 51.9%) and clinical pregnancy rates (69.0%, 59.4% versus 44.2%) than Group C. The implantation rate was significantly higher in Group B than in Groups A and C (59.4% versus 45.7%, 43.5%). The live birth rate was significantly higher in Group A than in Group C (59.2% versus 48.1%). The multiple pregnancy rate was significantly higher in Group A than in Groups B and C (34.4% versus 1.6%, 1.5%). The early miscarriage rate was significantly higher in Group C than in Group A and Group B (23.5% versus 8.7%, 12.7%). Premature delivery rates, late miscarriage rates and ectopic pregnancy rates were comparable across groups.

A single good quality day 6 blastocyst transfer was the preferable strategy for the freeze-all strategy patients who younger than 35 and without day 5 blastocyst formation.