INTRODUCTION:
Anencephaly is a malformation incompatible with life that generates ethical dilemmas. In 2012, the Supreme Federal Court of Brazil, via Claim of Non Compliance with a Fundamental Precept 54, declared the unconstitutionality of the punishment for pregnancy interruption in these cases. This study analyzes the impact of this decision on the rates of live births with anencephaly and legal abortions in Brazil.

METHODS:
This is an ecological time series study with annual data from 2000 to 2024. Data on live births with anencephaly were extracted from the Live Birth Information System and legal abortions from the Hospital Information System, both made available by the Department of Informatics of the Unified Health System. Interrupted time series analysis was applied, considering 2012 as the intervention, to estimate trends and level changes in rates per 10000 live births.

RESULTS:
Between 2000 and 2011, legal abortions grew + 0.37 per year. In 2012, there was an immediate level reduction of 4.40 cases per 10000 live births (p = 0.005). For anencephaly, the post-2012 trend showed a reduction of 0.055 cases per 10000 per year (p < 0.001), indicating a structural change in the temporal pattern and divergence from the estimated counterfactual scenario without the intervention.

CONCLUSIONS:
The decision of the Supreme Federal Court of Brazil in the Claim of Non-Compliance with a Fundamental Precept 54 is associated with measurable changes in indicators, stabilizing legal abortions after an initial drop and reducing the trend of births with anencephaly. Normative interventions produce relevant sanitary effects, promoting equity and the protection of human dignity according to Intervention Bioethics.