There is a well-established association between maternal depression and anxiety during pregnancy and adverse neurodevelopmental outcomes for children, including cognitive, emotional and behavioural problems. Women with severe anxiety and depression may be prescribed antidepressants in pregnancy, with the expectation that this would not only benefit the mothers but may also protect children from the adverse effects of maternal mental illness. Unfortunately, antidepressant use in pregnancy has itself been linked to adverse neurodevelopmental outcomes, but it is unclear to what extent this association is mediated by the underlying maternal illness. There is limited research on the relative effects of medicated versus non-medicated antenatal maternal depression/anxiety on child development, and the ALSPAC cohort study provides an opportunity to address this gap.