Pregnancy outcomes after fresh and frozen embryo transfer in women of advanced age and analysis of influencing factors: single-center experience.

OBJECTIVE

To investigate the differences in pregnancy outcomes between fresh embryo transfer (ET) and frozen embryo transfer (FET) in women of advanced age undergoing assisted reproductive technology (ART), and to provide evidence for optimizing embryo transfer strategies.

METHODS

This retrospective study included 359 women of advanced age (35-45 years) who underwent fresh ET and 605 who underwent FET at the Department of Reproductive Medicine, Lianyungang Maternal and Child Health Hospital from January 2019 to April 2025. Following 1:1 propensity score matching, 288 fresh ET and 288 FET cycles were analyzed. Clinical pregnancy rate, miscarriage rate, live birth rate, preterm birth rate, and neonatal birth weight were compared between the two groups. Multivariable logistic regression was used to identify factors associated with live birth, and conditional logistic regression was performed.

RESULTS

In the matched cohort, miscarriage rate and preterm birth rate were comparable between two groups (both P > 0.05). Fresh ET showed a tendency to increase the clinical pregnancy rate (P = 0.056) and significantly higher live birth rate (28.13% vs. 20.49%, P = 0.033). However, multivariate analysis showed that fresh ET had a higher live birth rate trend than FET (OR = 1.46, P = 0.072). Independent factors associated with increased live birth rate were younger female age, transfer of two embryos and transfer good-quality embryos (OR = 0.80, P < 0.001; OR = 2.35, P < 0.001; OR = 2.25, P < 0.017; respectively). These findings were further confirmed in a sensitivity analysis using conditional logistic regression accounting for matched pairs, in which transfer strategy remained non-significant (P = 0.344), while female age and transfer of two embryos remained significant predictors. Regarding perinatal outcomes, no significant differences were observed between the two groups for singleton deliveries in terms of gestational age, birth weight, macrosomia, or newborn sex (all P > 0.05).

CONCLUSION

In women of advanced age, the transfer strategy was not an independent predictor of live birth. Instead, younger maternal age and transfer of two embryos were the key factors to improved live birth outcomes.