Stillbirth in Iceland 1996-2021: Incidence and etiology.

Introduction: This study describes the stillbirth rate (SBR) in Iceland 1996-2021 and the causes of stillbirth according to the Stockholm classification of stillbirth, comparing time periods and gestational age (GA) groups.

Material and methods: Clinical information was obtained from medical records of mothers who had stillbirths and their infants (n = 395). Infants were divided into groups according to GA at diagnosis of stillbirth: early preterm: ≥22 but <28 weeks (n = 140), late preterm: ≥28 but <37 weeks (n = 130), and term: ≥37 weeks (n = 125). Autopsy records and gross descriptions of the placenta were reviewed, and microscopic slides were reevaluated, and findings classified according to the Amsterdam Consensus. Primary and associated causes of death were assigned according to the Stockholm classification of stillbirth. The SBR, maternal and fetoplacental characteristics, and causes of death were compared between two 13-year periods (1996-2008 and 2009-2021) and between GA groups.

Results: The SBR decreased from 4.10 to 2.88/1000 births (p = 0.009) between the two periods, but this decrease was limited to stillbirths diagnosed before term. Fewer stillbirths in the latter period were attributed to causes such as infection and placental abruption, and unexplained stillbirths reduced (0.59 vs. 0.16/1000, p < 0.05). The most common primary causes of stillbirth were reduced circulation in the umbilical cord (25.6%) and placental insufficiency (25.2%); both increased in incidence with more advanced gestation. Despite no difference in small-for-gestational-age infants, a larger percentage of stillbirths had low placental weight (21.3% vs. 30.3%, p = 0.002) and high fetoplacental ratio for GA (15.7% vs. 24.2%, p = 0.005) in the latter period, when a larger proportion of stillbirths were attributed to placental insufficiency (17.0% vs. 37.0%, p = 0.0002).

Conclusions: The SBR decreased in the latter period due to a reduction in preterm stillbirth, whereas the SBR at term was unchanged. Reduced circulation of the umbilical cord and placental insufficiency were the commonest causes, and both increased with GA. Stillbirth due to infection and placental abruption, as well as unexplained stillbirths, decreased during the study period, whereas deaths attributed to placental insufficiency became more common, reflecting a lack of reduction of stillbirth at term in the latter period.