Association between pre-pregnancy tobacco smoking and postpartum depression: A nationwide cohort study

Background: Prior literature examining the association between cigarette smoking and postpartum depression (PPD) has focused primarily on smoking behaviors during pregnancy or postpartum. However, there is a dearth of studies assessing pre-pregnancy smoking in relation to PPD.Method: A retrospective national cohort data from the National Health Insurance of South Korea were analyzed. A total of 392,394 women who gave birth between 2011 and 2015 and received health checkups within a year before pregnancy without a history of diagnosed depression were included. During the health checkup, partic-ipants self-reported their smoking status, amount, and duration in a health questionnaire. The diagnosis of PPD was defined by ICD-10 codes F32 and F33 during hospital visits within two years postpartum.Result: Overall, 24,441 (6.2 %) women were newly diagnosed with depression within two years postpartum. Those who reported that they had quit smoking or were currently smoking before pregnancy were more likely to be diagnosed with PPD compared to nonsmokers. A greater number of cigarettes smoked was associated with a higher risk of PPD for both current and former smokers. Results of cumulative lifetime smoking exposure demonstrated that even those with 2 pack-years of smoking had an increased risk of developing PPD within two years postpartum (HR: 1.44, 95 % CI: 1.29-1.60). Those who smoked >10 pack-years had the highest risk of developing PPD (HR: 1.86, 95 % CI: 1.14-3.04) compared to nonsmokers.Conclusion: Greater amount and duration of cigarette smoking in pre-pregnancy can increase the risk of PPD.