Risk factors for perinatal mortality associated with spontaneous preterm birth at a large tertiary hospital in New Zealand: a case-control study.

Abstract

Background: Perinatal death from spontaneous preterm birth (SPTB) varies by place of residence in New Zealand. Modifiable risk factors provide potential to prevent perinatal death due to preterm birth, and identification of women at risk, facilitates optimisation of care associated with early birth. The aim of this study was to identify risk factors for perinatal death due to spontaneous preterm birth in a multi-ethnic tertiary hospital population with high perinatal mortality. Methods: Case control study, cases being singleton non-anomalous perinatal deaths from 20 weeks gestation due to spontaneous preterm birth from 2014-2016 at Middlemore Hospital, South Auckland, New Zealand. Controls were the two subsequent singleton non-anomalous live births of any gestation in the same population. Data obtained from perinatal mortality and hospital databases and clinical records pertaining to risk factors in the first 20 weeks of gestation. Findings: Forty-two deaths from 20–36 weeks (95% at 20-24 weeks) and 84 control live births (3 preterm, 81 term). Previous spontaneous preterm birth (OR 3.90 (95%CI 1.39, 10.99)), extreme previous spontaneous preterm birth at ≤28 weeks (OR 8.20 (95%CI 1.62, 41.46)), nulliparity (OR 4.14 (95%CI 1.89, 9.09)), and BMI <19 (OR of 13.8 (95%CI 1.5, 130)) were associated with perinatal death from spontaneous preterm birth. 28% of cases and 7% of controls used other drugs (mostly alcohol) (OR 4.98 (95%CI 1.68-14.73)) and 31% of cases and 24% of controls smoked tobacco (OR 1.63 (95%CI 0.66, 4.03)). There were no significant associations with ethnicity, socioeconomic status, or with urinary or chlamydial infection in this population. Cases were screened for urinary (83% v 55%) and chlamydial (71% v 36%) infections more often than controls. Conclusion: Previous extreme spontaneous preterm birth was a major risk factor for perinatal death due to spontaneous preterm birth. Further research is required to understand risks in high deprivation multi-ethnic communities, which may differ from those in advantaged communities.