Hypoxic ischemic encephalopathy in offspring of immigrant women in Sweden: A population-based cohort study

Abstract

Introduction: One in four women giving birth in Sweden is foreign-born. Immigrant status has been suggested as a risk factor for adverse perinatal outcomes. It is not known if infants to foreign-born women have an increased risk of severe birth asphyxia, or which factors might mediate such association. Material and methods: A population-based cohort study of 726 730 live births at 36 weeks of gestation or more in Sweden in 2009–2015. The exposure was maternal country of birth, grouped according to the World Bank country classification: low-, lower-middle, upper-middle, and high-income economies. The main outcome was neonatal hypoxic ischemic encephalopathy (HIE). The outcome was estimated by severity and classified as non-hypothermia-treated HIE, representing mainly mild cases, and hypothermia-treated HIE, representing moderate to severe cases. A secondary outcome was low Apgar score at 5 minutes, defined as <7 or <4. Odds ratios with 95% CI were calculated, using Swedish-born women as the reference. Structural equation modeling was used to investigate potential mediation of known antepartum risk factors. Results: A total of 854 infants were diagnosed with HIE and 398 received therapeutic hypothermia. Offspring of mothers born in low-income countries had the highest incidences of HIE and low Apgar score, with an incidence of therapeutic hypothermia of 1.1 per 1000. Compared with offspring of Swedish-born mothers, these neonates had an almost two-fold increased risk of HIE, with or without hypothermia treatment (odds ratio 1.7; 95% CI 1.2–2.7 and odds ratio 1.7; 95% CI 1.2–2.6, respectively), and a 2- to 3-fold increased risk of low Apgar score. The structural equation model analysis indicated an exclusive direct effect of country of birth on HIE. Factors reflecting socio-economic status mediated a small proportion of the risk of Apgar score <7 at 5 minutes. Conclusions: Offspring of women born in low-income countries had associations with severe birth asphyxia, with increased risk of both HIE and low Apgar score at 5 minutes. The associations seemed only to be marginally mediated by other antepartum factors. The associations are complex and further studies are needed to find explanatory and potentially preventable factors.