Day 5 vs day 6 single euploid blastocyst frozen embryo transfers: which variables do have an impact on the clinical pregnancy rates?

Abstract

Objective: To determine which variables affect most the clinical pregnancy rate with positive fetal heartbeat (CPR FHB+) when frozen embryo transfer (FET) cycles are performed with day 5 (D5) or day 6 (D6) euploid blastocysts. Design and method A single center retrospective study was performed from March 2017 till February 2021 including all single FET cycles with euploid D5 or D6 blastocysts and transferred in natural cycles (NC) or hormone replacement therapy (HRT) cycles. Trophectoderm (TE) and inner cell mass (ICM) qualities were recorded before biopsy.

Results: A total of 1102 FET cycles were included, 678 with D5 and 424 with D6 blastocysts. Pregnancy rate (PR), clinical PR (CPR), and CPR FHB+ were significantly higher with D5 blastocysts (PR: 70.7% vs 62.0%, OR = 0.68 [0.53-0.89], p = 0.004; CPR: 63.7% vs 54.2%, OR = 0.68 [0.52-0.96], p = 0.002 and CPR FHB+: 57.8% vs 49.8%, OR = 0.72 [0.53-0.96], p = 0.011). However, miscarriage rate (12.5% vs 11.4%, OR = 0.78 [0.48-1.26], p = 0.311) did not differ. From a multivariate logistic regression model, endometrial thickness (OR = 1.11 [1.01-1.22], p = 0.028), patient's age (OR = 1.03 [1.00-1.05], p = 0.021), BMI (OR = 0.97 [0.94-0.99], p = 0.023), and ICM grade C (OR = 0.23 [0.13-0.43], p < 0.001) were significant in predicting CPR FHB+.

Conclusion: Although clinical outcomes are higher with D5 blastocysts, CPR FHB+ is more affected by endometrial thickness, patient age, BMI, and ICM grade C rather than biopsy day or endometrial preparation protocol.

Keywords: Day 5; Day 6; Embryo quality; Endometrial preparation; Frozen-embryo transfer; PGT-A.

Conflict of interest statement

The authors declare no competing interests.

© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

Figures

Fig. 1

Multinomial logit model representation including all variables affecting CPR FHB+outcome in FET cycles with euploid blastocyst. Variables affecting CPR FHB+ outcomes are represented in the Y axis and logarithm of the odds ratio are represented in the X axis. Variables not crossing the zero of the X axis are considered statistically significant (p < 0.05). As it is shown in the figure, ICM quality C is the most significant variable affecting CPR FHB+ in a negative way (CI on the left side compared to the central zero line). HRT, hormone replacement therapy; NC, natural cycle; AMH, Antimüllerian hormone; BMI, body mass index; ICM, inner cell mass; TE, trophectoderm; CI: 95% confidence intervals