[Contributions by the investigation of fetal deaths for improving the definition of underlying cause of death in the city of São Paulo, Brazil].

This study aimed to analyze the time trend in stillbirth rate (SBR) and the contribution by investigation to improving the definition of underlying cause of stillbirth in the city of São Paulo, Brazil, according to the place where the death certificate was issued. An ecological approach was used to analyze the trend in SBR by weight stratum (< 2,500g and ≥ 2,500g) and total deaths in the city in 2007-2017. Prais-Winsten generalized linear regression was used. The study of cases analyzed the underlying causes of stillbirth from 2012 to 2014, before and after the investigation, time of conclusion of the investigation, and redefinition of the underlying cause of stillbirths by type of issuer. In deaths with < 2,500g, there was an upward trend in SBR of 1.5% per year and a reduction (-1.3% per year) in stillbirths ≥ 2,500g. Total deaths presented a stable trend. In 2012-2014, 90% of deaths with ≥ 2,500g were investigated. After investigation, the underlying cause of death was redefined in 15% of the deaths, and not otherwise specified stillbirth (P95) represented 25% of the causes of death. The highest proportion of changes in the underlying cause of death occurred in deaths for which the death certificate was issued by the death certification review service (17%), while in health services the proportion was 10.6%. In conclusion, the SBR in deaths with ≥ 2,500g showed a downward trend. There was a significant redefinition of underlying causes, especially in those attested by the death certification review service. However, the redefinition was insufficient to expand the proportion of causes of death that would allow a better understanding of the mortality conditions.