Association between women's age and stage, morphology, and implantation of the competent blastocyst: a multicenter cohort study.

OBJECTIVE: To study if the age of women undergoing assisted reproductive technology treatment associates with stage, morphology, and implantation of the competent blastocyst. DESIGN: Multicenter historical cohort study based on exposure (age) and outcome data (blastocyst stage and morphology and initial human chorionic gonadotrophin [hCG] rise) from women undergoing single blastocyst transfer resulting in singleton pregnancy/birth. SETTING: Sixteen private and university-based facilities. PATIENT(S): In this study, 7,246 women who, between 2014 and 2018, underwent controlled ovarian stimulation (COS) or frozen-thawed embryo transfer (FET) with a single blastocyst transfer resulting in singleton pregnancy were identified. Linking data to the Danish Medical Birth Registry resulted in a total of 4,842 women with a live birth being included. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The competent blastocyst development stage (1-6), inner cell mass (A, B, C), trophectoderm (A, B, C), and initial serum hCG value. RESULT(S): Adjusted analysis of age and stage in COS treatments showed that for every 1-year increase in age there was a 5% reduced probability of the competent blastocyst assessed as being in a high stage at transfer. Comparison between hCG values in women 18-24 years and 25-29 years in both COS and FET showed significantly lower levels in the youngest women. CONCLUSION(S): The initial hCG rise was influenced by the age of the woman, with an identical pattern for hCG values in COS and FET treatments. In COS, the competent blastocyst had a reduced stage with increasing women's age.