Interaction of oxytocin level and past depression may predict postpartum depressive symptom severity

We examined plasma oxytocin concentration and postpartum depression (PPD) symptom severity in women who were not depressed during pregnancy and whether this differed by major depressive disorder (MDD) history. We assessed psychiatric history and plasma oxytocin in 66 healthy pregnant women in the third trimester (M = 35 ± 3 weeks) and depressive symptoms at 6 weeks postpartum (M = 5.9 ± 0.8 weeks). Linear regression analysis was used to examine oxytocin and PPD symptom severity and moderation of oxytocin and PPD by past MDD. Women with (n = 13) and without (n = 53) past MDD differed in third trimester depressive symptom severity, but not oxytocin level, demographic factors, or birth outcomes. Controlling for third trimester depressive symptoms, oxytocin level was unrelated to PPD symptom severity [B(SE) = -.019 (.084); β = -.025; t = -.227; p = .821]. However, oxytocin level interacted with past MDD to predict PPD symptom severity [B(SE) = 7.489 (2.429); β = .328; t = 3.084; p = .003]. Higher oxytocin predicted greater PPD symptom severity in women with past MDD (p = .019), but not in women without (p = .216). Replication in a larger sample and methodologic challenges are discussed.