Stillbirth rates following the change in definition of fetal mortality in Quebec.

Objectives: In 2019, Quebec changed its stillbirth definition to include fetal deaths at 20 weeks gestation or more. Previously, the criterion was a minimum birth weight of 500 g. We assessed the impact of the new definition on stillbirth rates.

Methods: We conducted a retrospective study of stillbirth rates between 2010 and 2021 in Quebec. The exposure consisted of the period during the new definition versus the preceding period. We assessed how the new definition affected stillbirth rates using interrupted time series regression, and compared the period during the new definition with the preceding period using prevalence differences and prevalence ratios with 95% confidence intervals (CI). We determined the extent to which fetuses at the limit of viability (under 500 g or 20‒23 weeks) accounted for any increase in rates.

Results: Stillbirth rates went from 4.11 before the new definition to 6.76 per 1000 total births immediately after. Overall, the change in definition led to an absolute increase of 2.58 stillbirths per 1000 total births, for a prevalence ratio of 1.76 (95% CI 1.61‒1.92) compared with the preceding period. Fetal deaths due to congenital anomalies increased by 6.82 per 10,000 (95% CI 4.85‒8.78), while deaths due to pregnancy termination increased by 10.47 per 10,000 (95% CI 8.04‒12.89). Once the definition changed, 37% of stillbirths were under 500 g and 42% were between 20 and 23 weeks, with around half of these caused by congenital anomalies and terminations.

Conclusion: Stillbirth rates increased after the definition changed in Quebec, mainly due to congenital anomalies and pregnancy terminations.