Determinants of increases in stillbirth rates from 2000 to 2010

Abstract

Background: After decades of decline, stillbirth rates have increased in several industrialized countries in recent years. We examined data from the province of British Columbia, Canada, in an attempt to explain this unexpected phenomenon.

Methods: We carried out a retrospective population-based cohort study of all births in British Columbia from 2000 to 2010. Outcomes of interest included overall stillbirth rates, birth weight-and gestational age-specific stillbirth rates, rates of spontaneous stillbirths (excluding pregnancy terminations that satisfied the definition of stillbirth [fetal death with a birth weight ≥ 500 g or gestational age at delivery ≥ 20 wk], hereafter referred to as "pregnancy terminations") and rates of congenital anomalies among live-born infants. We used logistic regression to adjust for changes in maternal age, parity, weight before pregnancy and multiple births.

Results: Overall, stillbirth rates increased by 31% (95% confidence interval [CI] 13% to 50%), from 8.08 per 1000 total births in 2000 to 10.55 per 1000 in 2010. The rate of stillbirths with a birth weight of less than 500 g increased significantly (p(trend) = 0.03), whereas the rate of stillbirths with a birth weight of 1000 g or more decreased significantly (p(trend) = 0.009). The rate of spontaneous stillbirths decreased nonsignificantly by 16%, from 5.7 per 1000 total births in 2000 to 4.8 per 1000 in 2010. There was a significant decline of 30% (95% CI 6% to 47%) in the rate of spontaneous stillbirth with a birth weight of 1000 g or more between 2000 and 2010; adjustment for maternal factors did not appreciably change this temporal effect. The prevalence of congenital anomalies among live-born infants decreased significantly, from 5.21 per 100 live births during the first 3 years (2000-02) to 4.77 per 100 during the final 3 years (2008-10).

Interpretation: Increases in pregnancy terminations were responsible for the increases observed in stillbirth rates and were associated with declines in the prevalence of congenital anomalies among live-born infants.

Figure 1:

Rates of all stillbirths and of spontaneous stillbirths (excluding pregnancy terminations) in British Columbia, from 2000 to 2010. Total births (live births and stillbirths) served as the denominator.

Figure 2:

Stillbirth rates by gestational age in the first 3 years of the study period (2000–02) and the last 3 years (2008–10). *Excludes pregnancy terminations.