Drinking or not drinking in pregnancy: the multiplicity of confounding influences.

AIMS Studies investigating associations between prenatal exposure to low-moderate doses of alcohol and mental health development in childhood are inconsistent. The aim of the present study was to compare women who drink and who do not drink alcohol in pregnancy on a number of potential confounding variables, and to investigate whether any latent variables could be identified among these. METHODS Data were obtained from the Danish National Birth Cohort. EXPOSURE cumulated alcohol intake in full pregnancy (n = 63,464). The women were subdivided into intake groups 0, >0-10, >10-30, >30-90 and >90 units of alcohol in full pregnancy. Hereafter, the abstainers were subdivided into an all-time and a pregnancy-abstaining group, and the high intakers (>90) were subdivided into a high (>90-180) and a very high (>180) intake group. OUTCOME self-reported and register-based information on socio-demographic and lifestyle factors, and latent variables from an exploratory factor analysis. RESULTS Significant differences were observed between the intake groups on virtually all parameters. Significant differences were observed between the abstaining groups and the high-intake groups. The exploratory factor analyses identified a number of latent variables between the potential confounding variables. CONCLUSION Differences on confounding factors may in part explain the lack of consistency in the literature investigating prenatal exposure to low-moderate doses of alcohol and mental health development. It is cautiously concluded that the failure to control for these factors introduces residual and/or unmeasured confounding into the analyses, and thus masks the potential (small) effect of being exposed to low doses of alcohol in pregnancy. It is recommended that future studies control for factor scores rather than for the observed variables as is practice today.