Legal framework and IVF outcomes: a comparative analysis of fresh and frozen embryo transfers in Switzerland.

Research Question: To what extent do legislative measures impact standard reproductive outcome parameters?

Design: Retrospective cohort study using data from the Swiss national IVF registry analysing the outcomes of 13,908 women undergoing embryo transfers resulting from their first lifetime oocyte retrieval before (2014-2016) or after (2020-2022) revision of the legislation, allowing extended culture for 12 zygotes. Live birth rates (LBR) and cumulative LBR (cLBR) were compared in fresh and frozen embryo transfer strategies in both periods. Adjusted multivariable mixed model analyses were performed to determine OR and incidence rate ratios (IRR).

Results: Before revision of the legislation, LBR was higher for fresh embryo transfers compared with frozen embryo transfers (27.2% versus 22.7%; P = 0.006). After revision of the legislation, LBR was lower for fresh embryo transfers (29.3% versus 36.3%; P < 0.001), and cLBR was higher for the freeze-all embryo transfer strategy (59.0% versus 39.8%; P < 0.001). However, in a multivariable analysis, no difference in the odds of live birth was found between fresh and frozen embryo transfers (OR = 1.08, 95% CI 0.95-1.22), and the freeze-all embryo transfer strategy was not found to be more effective than the fresh embryo transfer strategy (IRR = 1.12, 95% CI 0.98-1.27). In a subgroup analysis, fresh blastocyst embryo transfers showed higher LBR than cleavage stage embryo transfers (OR = 2.01, 95% CI 1.62-2.49).

Conclusion: The change in national legislation provided the unique opportunity to evaluate the legal impact on reproductive outcomes. Besides a reduction in the number of multiple births, LBR in frozen embryo transfers improved, resulting in comparable success of fresh and frozen embryo transfer strategies. In addition to technological improvement, the legal framework influences the evolution of clinical practice, thereby contributing to enhanced reproductive outcomes.