Background Low social support is consistently associated with postpartum depression. Previous studies do not always control for previous mental health and do not consider what type of support (tangible, emotional, informational or positive social interaction) is most important. The objectives are: to examine if low social support contributes to subsequent risk of depressive or anxiety symptoms and to determine which type of support is most important.

Methods Data from the All Our Families longitudinal pregnancy cohort were used (n=3057). Outcomes were depressive or anxiety symptoms at 4 months and 1 year postpartum. Exposures were social support during pregnancy and at 4 months postpartum. Log binomial models were used to calculate risk ratios (RRs) and absolute risk differences, controlling for past mental health.

Results Low total social support during pregnancy was associated with an increased risk of depressive symptoms (RR 1.50, 95% CI 1.24 to 1.82) and anxiety symptoms (RR 1.63, 95% CI 1.38 to 1.93) at 4 months postpartum. Low total social support at 4 months was associated with an increased risk of anxiety symptoms (RR 1.65, 95% CI 1.31 to 2.09) at 1 year. Absolute risk differences were largest among women with previous mental health challenges resulting in a number needed to treat of 5 for some outcomes. Emotional/informational support was the most important type of support for postpartum anxiety.

Conclusion Group prenatal care, prenatal education and peer support programmes have the potential to improve social support. Prenatal interventions studies are needed to confirm these findings in higher risk groups.