MedWire News: Children born to mothers who smoke during pregnancy have an increased risk for non-clinical psychotic experiences, say UK scientists in findings that may help to highlight the effect of substances on cerebral development and function.

Substance use during pregnancy is associated with a range of adverse outcomes in offspring, including psychopathological effects. However, it is difficult to conclude that such associations are causal from the studies that have been conducted thus far.

Stanley Zammit, from Cardiff University, and colleagues therefore studied 6356 adolescents aged 12 years from the Avon Longitudinal Study of Parents and Children birth cohort who completed a semi-structured interview for psychotic symptoms.

In all, 11.6% of the sample were rated as having suspected or definite psychotic-like symptoms, and 4.7% were identified as having definite symptoms, the team reports in the British Journal of Psychiatry.

Maternal tobacco use during pregnancy was strongly associated with any suspected or definite psychotic-like symptoms in the offspring, at an adjusted odds ratio of 1.20. Paternal smoking and maternal smoking post-pregnancy were not significantly associated with symptoms. Interestingly, maternal smoking in the third, as opposed to the first, trimester was associated with an increased risk for symptoms, at an odds ratio of 2.1.

While maternal cannabis during pregnancy use was not significantly associated with psychotic-like symptoms in offspring, there was a non-linear effect of alcohol use during pregnancy on the risk for symptoms, at an odds ratio of 1.24 per 10-unit increase in alcohol use per week. However, these associations were eliminated when women who drank >21 units per week were excluded from the analysis.

The team notes: “If our results for the association between maternal smoking and psychotic-like symptoms are non-biased and truly reflect a causal relationship, we can estimate that about 20% of adolescents in this cohort would not have developed psychotic symptoms if their mothers had not smoked.

“Therefore, although the effect size of association for maternal smoking is rather modest, the frequency of this exposure means that maternal smoking may nevertheless be an important risk factor for the development of psychotic experiences in the population.”

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