In the peripartum period, the literature on seasonality in depression is still scarce and studies present varying findings. The aims of this study were to investigate whether seasonal patterns in postpartum depressive symptoms previously identified in a Swedish study could be replicated in a larger study, as well as to assess seasonal patterns in depressive symptoms during pregnancy.

This was a nested case-control study comprised of 4129 women who participated in the BASIC project and gave birth at Uppsala University Hospital, Uppsala, Sweden, between February 2010 and December 2015.

Women who gave birth in October–December 2011 had an increased odds of depressive symptoms at 6 weeks postpartum, when compared with women giving birth in April–June 2011 (aOR = 2.42; 95% CI: 1.12–5.26). The same pattern was found among women with a history of depression. No other seasonal patterns for depressive symptoms during pregnancy or at 6 weeks postpartum were identified.

In general, no consistent seasonal patterns were found in peripartum depressive symptoms. Whether the seasonal patterns found in some studies during certain years may be due to other factors relating to specific years and seasons, such as extreme climatic conditions or other particular events, warrants further investigation.