Preterm birth and long-term risk of psychiatric disorders in Quebec: a population-based cohort study using administrative data

Background: Past evidence supports an association between preterm birth and psychiatric disorders. However, most of these studies are based on European cohorts, with relatively few from North America and especially Canada. Additionally, the effect modification by sex and socioeconomic status (SES) has been understudied. Identifying whether individuals born preterm are at risk of psychiatric disorders is important to inform programs that improve functioning and quality of life of preterm children and their families.Objective: The purpose of this study was to quantify associations between preterm birth and adolescent-to-adult psychiatric disorders in the province of Quebec, Canada, and whether sex or SES modified this relationship. Methods: We used an observational cohort study design based on linked administrative data. Our study population was all children born preterm in Quebec (gestational age <37 weeks; N=100,040) between 1976 and 1995 with valid data, matched 1:2 on sex and year of birth with term born children (i.e., 37-42 gestational weeks; N=203,340). We considered preterm birth as both a binary (<37 weeks gestational age) and categorical exposure (extreme, <28; very, 28-31; moderate-to-late, 32-36 weeks gestational age). We also used gestational age as a continuous exposure, in weeks.Main Outcomes and Measures: Individuals were followed from age 11 years until either incident inpatient/outpatient diagnosis of a psychiatric disorder (attention-deficit/hyperactivity disorder [ADHD], psychosis, bipolar disorder, anxiety, and depression), death, or December 2019. Cox proportional hazard models were used to investigate associations between preterm birth and the selected outcomes. The roles of sex and SES (material/social deprivation, and maternal education) as effect modifiers were investigated in interaction analyses.Results: A total of 303,375 individuals (46% females) were followed up from birth up to age 40 (5,161,915–6,721,222 person-years). Incidence rate of any psychiatric disorder was 2770 per 100,000 person-years in the preterm group, compared to 2561 per 100,000 person-years in the term group. Compared to those in the term group, those born preterm had a higher risk of experiencing all outcomes, with magnitudes ranging from HR 1.16 for ADHD (95% confidence interval 1.13,1.20) to 1.05 for anxiety (1.04,1.07). A dose-response relationship was observed, with increasing risks of ADHD, psychosis, and anxiety as the degree of prematurity increased. There was no clinically relevant evidence of effect modification by sex or SES. Discussion: This study reflects past evidence coming out of European administrative cohorts that children born preterm are at higher risk of being diagnosed with psychiatric disorders and that this association exists in a dose-response manner. This study adds to the evidence by finding this dose-response relationship in North America and specifically, the Canadian province of Quebec. The results, taken in the context of past literature, suggests that preterm birth is robustly linked to psychiatric disorders, and therefore, should be emphasized more in provincial and national guidelines as a risk factor for psychiatric disorders. As for the mixed results with regards to the effect modifying effect of sex and SES, more research is warranted to identify whether there are subgroups of preterm children particularly vulnerable to psychiatric disorders. Conclusion: Preterm children were more likely to be diagnosed with psychiatric disorders in adolescence-to-adulthood, with similar risks across sexes and socioeconomic strata of the population. Continued mental health surveillance in this more vulnerable group is important so that appropriate interventions can be timely initiated to improve well-being.

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