Objectives: Estimating associations between somatic and socioeconomic risk factors and post-discharge under-five mortality.
Design: Register-based national cohort study using multiple Cox regression.
Participants: The population of 1,263,795 Danish children live-born 1997-2016 who survived until date of first discharge to the home after birth was followed from that date until death, emigration, 5 years of age or 31 December 2016.
Main outcome measures: (A) Mortality hazard ratios (HRs) among all children, (B) mortality HRs among children without severe chronic disease, and (C) mortality HRs among children without severe chronic disease or asthma.
Main results: In the total population (1,947 deaths) severe chronic disease was associated with mortality HR = 15.28 (95% CI: 13.77-16.95). In children without severe chronic-disease (719 deaths) other somatic risk factors were immature birth HR = 3.40 (1.92-6.02), maternal smoking HR = 1.84 (1.55-2.18) and low birth weight HR = 1.74 (1.21-2.51). Socioeconomic risk factors for mortality included: maternal age < 25 years HR = 1.91 (1.38-2.64) compared to > 35 years (similar for 30-35 years and 25-29 years), lowest vs. highest family income tertile HR = 1.76 (1.23-2.51), not living with both parents HR = 1.63 (1.25-2.13), maternal unemployment HR = 1.54 (1.12-2.12), presence of siblings HR = 1.44 (1.20-1.71) and secondary vs. tertiary parental education HR = 1.33 (1.07-1.65) for fathers and HR = 1.23 (1.01-1.52) for mothers. Factors not found to be associated with child mortality in this population included presence of asthma HR = 1.29 (0.83-1.98) and non-Danish ethnicity HR = 0.98 (0.70-1.37).
Conclusions: Childhood death after discharge to the home after birth and before 5 years of age is a very rare event in Denmark. This 'post-discharge' mortality was heavily associated with severe chronic disease. In children without severe chronic disease, immature birth, maternal smoking and certain socioeconomic characteristics were noticeable risk factors. Mortality may possibly be decreased by focusing on vulnerable groups.