Maternal age at first birth and offspring criminality: using the children of twins design to test causal hypotheses

Abstract

Teenage childbirth is a risk factor for poor offspring outcomes, particularly offspring antisocial behavior. It is not clear, however, if maternal age at first birth (MAFB) is causally associated with offspring antisocial behavior or if this association is due to selection factors that influence both the likelihood that a young woman gives birth early and that her offspring engage in antisocial behavior. The current study addresses the limitations of previous research by using longitudinal data from Swedish national registries and children of siblings and children of twins comparisons to identify the extent to which the association between MAFB and offspring criminal convictions is consistent with a causal influence and confounded by genetic or environmental factors that make cousins similar. We found offspring born to mothers who began childbearing earlier were more likely to be convicted of a crime than offspring born to mothers who delayed childbearing. The results from comparisons of differentially exposed cousins, especially born to discordant monozygotic twin sisters, provide support for a causal association between MAFB and offspring criminal convictions. The analyses also found little evidence for genetic confounding due to passive gene-environment correlation. Future studies are needed to replicate these findings and to identify environmental risk factors that mediate this causal association.

Figure 1

Comparing linear and quadratic models predicting criminal convictions for unrelated offspring

Figure 1

Hypothetical patterns of results consistent with (A) a causal association, (B) a statistical association confounded by genetic factors, and (C) a statistical association confounded by environmental factors

Figure 2

Flowchart of participant inclusion and exclusion criteria

Figure 3

Hazard ratios with 95% CIs for ordinal survival models

Figure 4

Hazard ratios with 95% CIs for survival models with (A) linear measure of MAFB and (B) binary measure of MAFB (teenage versus adult first birth) as predictors of offspring criminal convictions