The association between body mass index and postpartum depression: A population-based study

Background: Postpartum depression (PPD) reportedly affects between 6.5–19% of all new mothers. Identifying those at greatest risk for PPD has implications for prevention, early detection and intervention. While the relationship between extremes of body mass index (BMI) and depression has been frequently studied, the association between BMI and PPD is less understood. Methods: Prospective cohort of all women with live singleton births in Sweden 1997–2008. We calculated the relative risk (RR) for PPD in relation to each woman's BMI and depression history. PPD diagnosis was based on a clinical diagnosis of depression within the first postpartum year. Results: First trimester BMI measurements were available for 611,506 women. Low BMI (< 18.5) RR_adj = 1.52, [95% CI: 1.30–1.78] and high BMI (> 35) RR_adj = 1.23, [95% CI: 1.04–1.45] were associated with increased PPD risk. Women with a depression history had an increased risk with low BMI (RR_adj = 1.51, [95% CI: 1.17–1.95]). Limitations: Only first births were analyzed, potentially underestimating PPD incidence. Clinical data from health registries offers limited resolution regarding the specificity of diagnoses and incomplete sensitivity if women do not seek care. Conclusions: First trimester of pregnancy BMI is associated with PPD risk. This risk is further modified by depression history. While low BMI places all women at risk for PPD, being overweight increases risk of PPD only in women without a history of depression. Future research should explore potentially modifiable mechanisms involved in the relationship between PPD and BMI and should also examine interventional strategies for pregnant women at the extremes of BMI and/or with a depression history.