Advancing maternal age worsens pregnancy outcomes following single frozen embryo transfer with preimplantation genetic testing.

RESEARCH QUESTION: What is the critical age for the onset of deterioration in pregnancy outcomes associated with advancing maternal age in frozen embryo transfer (FET) cycles following preimplantation genetic testing (PGT)?

DESIGN

This retrospective analysis included 6354 women (aged 20-45 years) who underwent PGT with single blastocyst transfer within 1 year of oocyte retrieval at a single centre, utilizing data collected from February 2017 to December 2024. Only the first FET cycle after oocyte retrieval was included, and fertilization was performed via intracytoplasmic sperm injection. Maternal characteristics were examined by transfer age; outcomes included clinical pregnancy rate (CPR), live birth rate (LBR), implantation rate, implantation failure rate (IFR) and abortion rate. Locally estimated scatterplot smoothing (LOESS) curves were used to visualize continuous trends. Restricted cubic spline (RCS) curves were used to assess age-related associations and non-linear effects. Threshold effect analysis identified the pivotal age at which endometrial aging has an adverse effect on outcomes.

RESULTS

Advancing maternal age at embryo transfer was associated with declining CPR and LBR, and increasing IFR and abortion rate. Non-linear associations between maternal age at embryo transfer and clinical pregnancy (P non-linear = 0.009), live birth (P non-linear = 0.026), and implantation failure (P non-linear=0.009) were identified based on RCS analysis. Each year beyond 33 years of age was associated with a relative 5.8% decrease in the likelihood of clinical pregnancy [adjusted hazard ratio (aHR) = 0.942, 95% CI 0.908-0.977; P = 0.001], a relative 7.2% decrease in the probability of live birth (aHR = 0.928, 95% CI 0.895-0.963; P = 0.006), and a relative 6.1% increase in the risk of implantation failure (aHR = 1.061, 95% CI 1.023-1.101; P = 0.001).

CONCLUSIONS

Endometrial aging may be associated with significantly worsened pregnancy outcomes in women aged >33 years.