What Were We Thinking (WWWT) is a gender-informed, psychoeducational programme to promote respectful relationships and skilled management of unsettled infant behaviours and thereby reduce postpartum common mental disorders. It comprises a highly structured seminar for couples and babies, usual primary care from a WWWT-trained nurse and take-home print materials. The aim was to assess long-term outcomes after a cluster randomised controlled trial of WWWT.

Trial participants who consented completed a computer-assisted telephone interview 18 months postpartum. Depressive symptoms were assessed with the Patient Health Questionnaire (PHQ-9) and anxiety symptoms with the Generalised Anxiety Disorder Scale (GAD-7). Impacts of baseline characteristics and trial arm on changes in scores from baseline to follow-up were calculated using Conditional Latent Growth Curve Models adjusting for prognostic indicators and controlling for clustering effects.

Overall, 314/400 (78.5%) women contributed data at baseline (6 weeks postpartum), trial endline (26 weeks postpartum) and follow-up (12 months after trial endline). In intention-to-treat analyses, there was a significantly greater improvement in adjusted GAD-7 scores [regression coefficient (RC) −0.55; 95% confidence interval (CI) −0.94 to −0.17] and non-significant improvement (RC −0.27; 95% CI −0.63 to 0.08) in PHQ-9 scores from baseline to follow-up in the intervention than the control arm. In a per-protocol analysis, the proportion with GAD-7 scores ⩽4 (asymptomatic) improved 24.1% (55.7% baseline to 79.8% follow-up, p = 0.043) among women who received the full WWWT programme, which included the seminar, compared with 2.4% (77.1–79.5%, p = 0.706) among those who received the partial intervention (usual care from WWWT-trained nurse and print materials).

The WWWT programme has a significant sustained beneficial impact on postnatal generalised anxiety among primiparous women compared with usual care. The in-person seminar is the most influential component of the intervention. Psycho-educational programmes integrated into primary care appear promising as a strategy to reduce postpartum common mental disorders.