Fetal growth and psychiatric and socioeconomic problems: population-based sibling comparison

Abstract

Background: It is unclear whether associations between fetal growth and psychiatric and socioeconomic problems are consistent with causal mechanisms.

Aims: To estimate the extent to which associations are a result of unmeasured confounding factors using a sibling-comparison approach.

Method: We predicted outcomes from continuously measured birth weight in a Swedish population cohort (n = 3 291 773), while controlling for measured and unmeasured confounding.

Results: In the population, lower birth weight (⩽ 2500 g) increased the risk of all outcomes. Sibling-comparison models indicated that lower birth weight independently predicted increased risk for autism spectrum disorder (hazard ratio for low birth weight = 2.44, 95% CI 1.99-2.97) and attention-deficit hyperactivity disorder. Although attenuated, associations remained for psychotic or bipolar disorder and educational problems. Associations with suicide attempt, substance use problems and social welfare receipt, however, were fully attenuated in sibling comparisons.

Conclusions: Results suggest that fetal growth, and factors that influence it, contribute to psychiatric and socioeconomic problems.

Fig. 1

Associations derived from continuous (line) and ordinal (bar with 95% confidence interval) representation of birth weight when predicting psychiatric outcomes. (a) Attention-deficit hyperactivity disorder (ADHD), (b) autism spectrum disorder (ASD), (c) psychotic or bipolar disorder, (d) suicide attempt, (e) substance use problems, and (f) criminality. Baseline, population-wide estimates are shown with the solid line and dark bars. Sibling-comparison, fixed-effects models are shown with dotted lines and light bars. Reference group are those born in the 3501-4000 g birth weight category. The maintenance of association magnitude across population and sibling-comparison models, consistent with a causal inference, can be noted when predicting ADHD, ASD and psychotic or bipolar disorder only. A protective effect can be noted when predicting criminality in the decrease of association in the sibling-comparison model.

Fig. 2

Associations derived from continuous (line) and ordinal (bar with 95% confidence interval) representation of birth weight when predicting socioeconomic outcomes. (a) Failing grades, (b) education under 10 years, and (c) social welfare receipt. Baseline, population-wide estimates are shown with the solid line and dark bars. Sibling-comparison, fixed-effects models are shown with dotted lines and light bars. Reference group are those born in the 3501-4000 g birth weight category. Although attenuated, the maintenance of association magnitude across population and sibling-comparison models, consistent with a causal inference, can be noted when predicting failing grades and education under 10 years only.