Morphological quality on Day 3 affects the pregnancy outcomes of low-quality euploid blastocysts: a retrospective cohort study.

STUDY QUESTION Does the morphological quality on Day 3 influence the pregnancy outcomes of euploid blastocysts? SUMMARY ANSWER The morphological quality on Day 3 affects the clinical pregnancy rate (CPR) and live birth rate (LBR) of low-quality euploid blastocysts. WHAT IS KNOWN ALREADY The morphological grading of Day 3 embryos affects the pregnancy outcome of cleavage-stage embryos and is an excellent indicator to predict embryo development potential. However, it is still unclear whether morphological quality on Day 3 is associated with pregnancy outcomes of the euploid blastocyst. STUDY DESIGN, SIZE, DURATION This retrospective cohort study comprised 1275 patients who received single euploid blastocyst transfer between January 2016 and August 2021 at a tertiary teaching hospital. PARTICIPANTS/MATERIALS, SETTING, METHODS Patients were grouped into two groups according to the morphological grading on Day 3 of transferred blastocysts: high-quality (HQ, including Grades I and II) Day 3 embryos and low-quality (LQ, Grade III) Day 3 embryos. The primary outcomes were CPR and LBR. Interactions of development days (Day 5 and Day 6) and morphological quality (high- and low-quality) of blastocysts with morphological quality of Day 3 embryos on pregnancy outcomes were tested in the stratified analysis and logistic regression models. The multivariate logistic regression analysis was conducted to investigate the independent effect of the morphological quality of Day 3 embryos on pregnancy outcomes after adjusting for potentially confounding factors. MAIN RESULTS AND THE ROLE OF CHANCE The CPR and LBR of the HQ Day 3 embryos group were statistically higher than those of the LQ Day 3 embryos group (CPR: 59.73% versus 49.70%, respectively, P  =   0.015; LBR: 49.73% versus 41.21%, respectively, P  =   0.041). The development days of blastocysts did not exhibit a multiplicative interaction with the morphological quality of Day 3 embryos on the CPR (P for interaction = 0.648) and LBR (P for interaction = 0.925). The morphological quality of blastocysts exhibits a multiplicative interaction with the morphological quality of Day 3 embryos on the CPR (P for interaction = 0.020) and LBR (P for interaction = 0.012). After adjusting for potential confounders, the HQ Day 3 embryo group was positively associated with the CPR (adjusted odds ratio (aOR): 2.10, 95% CI: 1.31–3.36, P  =   0.002) and LBR (aOR: 1.97, 95% CI: 1.20–3.25, P  =   0.008) of LQ blastocysts. However, the morphological quality on Day 3 was not significantly associated with the CPR (aOR: 0.95, 95% CI: 0.58–1.55, P  =   0.835) and LBR (aOR: 0.86, 95% CI: 0.53–1.40, P  =   0.550) of HQ blastocysts. LIMITATIONS, REASONS FOR CAUTION Selection and confounding bias introduced by the retrospective design cannot be completely eliminated in this study, although multivariable logistic analysis was conducted to adjust for potential confounders. Also, some subgroups had small sample sizes, which may reduce statistical power. Moreover, participants in our study only received single euploid blastocyst transfer, and whether the results could apply to blastocysts with unknown ploidy status is unclear. WIDER IMPLICATIONS OF THE FINDINGS This study found that the morphological quality on Day 3 was significantly associated with the CPR and LBR of LQ blastocysts; Therefore, when only LQ euploid blastocysts are available for transfer, blastocysts derived from HQ Day 3 embryos are recommended. STUDY FUNDING/COMPETING INTEREST(S) No external funding was obtained. The authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER N/A. [ABSTRACT FROM AUTHOR]