Freeze-only versus fresh embryo transfer in a multicenter matched cohort study: contribution of progesterone and maternal age to success rates

Objective To compare implantation and ongoing pregnancy rates in freeze-only versus fresh transfer cycles. Design Retrospective matched cohort study. Setting Not applicable. Patient(s) Women selected using a matching algorithm for similar distributions of clinical characteristics for a total of 2,910 cycles (1,455 fresh cohort and 1,455 freeze-only cohort). Intervention(s) None. Main Outcome Measure(s) Implantation and ongoing pregnancy rates. Result(s) Implantation and ongoing pregnancy rates were statistically significantly higher in the freeze-only transfer cohort than in the matched fresh transfer cohort: ongoing pregnancy rate for freeze-only was 52.0% (95% confidence interval [CI], 49.4–54.6) and for fresh was 45.3% (95% CI, 42.7–47.9), odds ratio (OR) 1.31 (95% CI, 1.13–1.51). In a stratified analysis, the odds of ongoing pregnancy after freeze-only transfer were statistically significantly higher for women both above and below age 35 with progesterone concentration >1.0 ng/mL (age ≤35: OR 1.38 [1.11–1.71]; age >35: OR 1.73 [1.34–2.24]). For women with progesterone concentration ≤1.0 ng/mL, no statistically significant difference in freeze-only odds of ongoing pregnancy was observed in either age group. The sensitivity analysis revealed that increasing maternal age alone (regardless of progesterone) trended toward a more beneficial effect of freeze-only cycles. A lower progesterone concentration was associated with statistically significantly higher ongoing pregnancy odds for fresh but not freeze-only cycles. Conclusion(s) Freeze-only transfer protocols are associated with statistically significantly higher ongoing implantation and pregnancy rates compared with fresh transfer cycles. This effect is most pronounced for cycles with progesterone >1.0 ng/mL at trigger and may also be stronger for older patients.