In Thailand, depression among adolescent mothers is poorly understood. A study of depression in adolescent mothers is important, particularly in the view of the potential impact of antepartum depression on the prediction of postpartum depression.

This prospective longitudinal study was designed to examine the rates of depression and the causal relationship among self-esteem, social support, and depression among a sample of Thai adolescent mothers.

A multi-stage random sampling was used to obtain a sample of 400 pregnant adolescents from four hospitals in Bangkok metropolitan area. Pregnant adolescent who met inclusion criteria were asked to complete three questionnaires: The Center for Epidemiologic Studies Depression Scale, the Rosenberg's Self-Esteem Scales, and the Inventory of Social Support Behaviors Questionnaire.

Data were collected during the third trimester of pregnancy and then at the sixth weeks postpartum. The researcher calculated percentages of adolescent mothers who meet cut-off depression scores. The SPSS and LISREL Program were used to test the hypotheses.

The research results showed that the rates of postpartum depression were higher than the rates of antepartum depression (54.71% (n=400), and 47.00%(n=340), respectively). The determinants in antepartum cross-sectional model could explained 38% of antepartum depression. All of determinants in longitudinal causal model could explained 63 % of postpartum depression (Relative chi-square = 128.17, RMSEA = .020, GFI =.96 and AGFI=.94).

The findings from this study not only promote early detection of depression but also contribute information about how self-esteem and social support are related to depression in Thai adolescent mothers. Such knowledge facilitates the development of nursing interventions to prevent or decrease depression in this population during the antepartum the postpartum periods.