P-233 Embryo transfer timing and clinical pregnancy success: a retrospective study
Authors: Dagher C , Depret-Bixio L , Saadeh D , Shmoury M , Fakih M 
Published: July 2024

Study question

The aim of this study is to compare the clinical outcome of day5 versus day6 genetically normal blastocyst transfers.

Summary answer

1000 oocytes were analyzed showing a highly significant difference in the number of normal embryos and clinical pregnancy rates in day5 versus day6 blastocysts

What is known already

studies have shown that day 5 embryos have a higher pregnancy rate compared to day 6 embryos, some studies had only euploid embryos transferred and others did not have any genetic testing done on embryos.

No study had a sample size as large as 1760 and the number of embryos studied was a limiting factor in their results.

Study design, size, duration

The study is a retrospective cross-sectional chart review with multivariate analysis, data from January 2019 up to February 2023 were extracted.

1760 patients were recruited, 1000 in the day5 group and 760 in the day6 group. The data recorded for each patient included maternal age, body mass index (BMI), anti-Müllerian hormone (AMH) level, number, prenatal genetic diagnostic testing, frozen embryo transfer, sperm parameters, and pregnancy status.

Participants/materials, setting, methods

All embryos were genetically tested for aneuploidy before transfer, using next-generation sequencing technology to rule out 24-chromosome aneuploidies (1-22, X, Y).

All patients who have single embryo transfer, frozen embryos and pre-implantation genetic diagnosis (PGD) were included in the study.

Continuous variables were expressed as mean with standard deviation and categorical variables as numbers and frequencies (percentages). Statistical differences between groups were estimated using the chi-square or Fisher’s test. All analyses were performed using SAS studio.

Main results and the role of chance

1,000 cycles were analyzed for Day 5 and 760 for Day 6 embryo.

The number of blastocysts formed, and genetically diagnosed embryos significantly favor the Day 5 group. There’s a significant difference in the number of normal embryos, with the Day 5 group having more. There is a highly significant difference in clinical pregnancy rates.

On the other hand, the differences in biochemical pregnancies are not statistically significant.

The occurrence of ectopic pregnancies shows no significant difference.

Additionally, there is no statistically significant difference in the rates of miscarriage.

There is a highly significant difference in blastocyst formation rates, with Day 5 embryos. This indicates that Day 5 embryos have a significantly higher likelihood of forming blastocysts compared to Day 6 embryos. Implantation: Day 5 embryos have an implantation rate of 62.0% compared to 49.7% for Day 6 embryos. Day 5 embryos exhibit a significantly higher likelihood of successful implantation. Euploid: The difference in euploid rates is statistically significant, albeit with a lower p-value of 0.0236. Day 5 embryos have a rate of 59.6%, while Day 6 embryos have a rate of 56.0%. Day 5 embryos are associated with a lower likelihood of being aneuploid

Limitations, reasons for caution

Limitation of this study is that we do not have data available regarding complications during pregnancy in the day 5 versus day 6 groups and we had no data regarding the the live birth rate between the two groups.

Wider implications of the findings

This study has the potential to revolutionize worldwide discussions during IVF consultations. With the large sample size we can provide for the first time a statistically significant difference in the percentage of success when transferring a day5 (61%) versus day6 (49%) euploid embryo.

Trial registration number

not applicable