Pre-conception and prenatal alcohol exposure from mothers and fathers drinking and head circumference: results from the Norwegian Mother-Child Study (MoBa).

Although microcephaly is a feature of Fetal Alcohol Syndrome, it is currently unknown whether low-to-moderate prenatal alcohol exposure affects head circumference. Small magnitude associations reported in observational studies are likely to be misleading due to confounding and misclassification biases. Alternative analytical approaches such as the use of family negative controls (e.g. comparing the effects of maternal and paternal exposure) could help disentangle causal effects. We investigated the association of maternal and paternal alcohol drinking before and early in pregnancy with infant head circumference, using data from 68,244 mother-father-offspring trios from the Norwegian Mother and Child Cohort Study (MoBa) (1999-2009). In analyses adjusted for potential confounders, we found no consistent pattern of association between maternal or paternal alcohol intake before or during pregnancy and offspring head circumference modelled as a continuous outcome. However, we found higher odds of microcephaly at birth for higher paternal, but not maternal, alcohol consumption before pregnancy, and similar but weaker effect estimates for first trimester drinking. Associations with paternal drinking before pregnancy were unexpected and should be regarded as hypothesis generating, until independently replicated, although potentially important given the absence of guidelines on safe drinking levels for men in couples trying for a pregnancy.