Conventional Versus Frozen Embryo Transfer in IVF/ICSI Cycles: A Systematic Review of Pregnancy Outcome

Although numerous studies have explored differences between conventional (fresh) and frozen embryo transfer in IVF/ICSI cycles, inconsistencies remain regarding their impact on neonatal outcomes. The objective of this systematic review was to comprehensively evaluate and compare pregnancy and neonatal outcomes—such as preterm birth, low birth weight, and growth parameters—between conventional embryo transfer (ET) and frozen embryo transfer (FET). A systematic literature search was conducted across major databases, including PubMed, Cochrane Library, Scopus, Web of Science, Wiley, Ovid, and ScienceDirect, covering publications from January 1980 to February 2025. Studies were included if they compared fresh and frozen embryo transfers in IVF/ICSI cycles and reported at least one neonatal or pregnancy outcome. Data extraction and quality assessment were performed independently by two reviewers using the Newcastle–Ottawa Scale (NOS) for cohort studies and the revised Cochrane Risk of Bias Tool for randomized controlled trials. Twenty-three eligible studies were identified, encompassing over 165,000 embryo transfer cycles from diverse geographic regions. The findings indicated that singleton pregnancies conceived after FET were associated with lower risks of preterm birth, low birth weight, and small-for-gestational-age infants compared to those conceived via fresh ET. Conversely, FET was linked with a higher likelihood of large-for-gestational-age and macrosomic births. RCTs and meta-analytic data further demonstrated higher clinical pregnancy and live birth rates and lower miscarriage and OHSS rates with FET. No significant differences were observed between the two groups in rates of congenital anomalies or neonatal mortality. This systematic review demonstrates that frozen embryo transfer is generally associated with more favorable neonatal outcomes than conventional fresh embryo transfer, particularly regarding fetal growth and gestational maturity. While FET offers distinct advantages, individualized treatment planning remains essential, and the decision to use fresh or frozen transfer should be based on patient characteristics and clinical context. Further prospective studies are encouraged to explore the long-term implications of both transfer methods on child health and maternal outcomes.