Wilcox M, McGee BA, Ionescu DF, et al. - Given a lack of information concerning the onset and course of perinatal depression, a serious, prevalent heterogeneous syndrome that can occur during the period from conception through several months after childbirth, researchers conducted a longitudinal study of the disorder including the antenatal period in population-based samples. An Internet panel of pregnant women recruited in 2 cohorts was used for this work; 858 ascertained in the first and 322 ascertained in the third trimesters of pregnancy. The second cohort was selected to ensure an adequate sample to investigate depressive symptoms later in pregnancy and in the postpartum period. Depressive symptoms were reported at pregnancy inception in approximately 10% of women. Nearly the same prevalence was observed at 4 weeks and 3 months postpartum. During pregnancy, an increase in prevalence to 16% was observed in the third trimester. Predictors of incident depressive symptoms and covariates correlated with time-to-onset were health history (psychiatric and medical) and social support covariates. Eighty percent of the incident cases befell during pregnancy, with 1/3 befalling in the first trimester. This finding emphasizes screening for mental health early in pregnancy and throughout gestation.