Pregnancy complications and poor birth outcomes can affect the survival and long-term health of children. The preconception period represents an opportunity to intervene and improve outcomes; however little is known about women's mental health prior to pregnancy as a predictor of such outcomes. We sought to determine if and to what extent women's preconception mental health status impacted subsequent pregnancy complications, non-live birth, and birth weight using a nationally representative, population-based sample. We used pooled 1996-2006 data from the nationally-representative Medical Expenditure Panel Survey (MEPS). Poor preconception mental health was defined as women's global mental health rating of "fair" or "poor" before conception. Logistic regression was used to assess the association between preconception mental health and pregnancy complications, non-live birth, and having a low birth weight baby within the follow up period. Poor preconception mental health was associated with increased odds of experiencing any pregnancy complication (AOR 1.40, 95% CI: 1.02-1.92), having a non-live birth (AOR 1.48, 95% CI: 0.96-2.27), and having a low birth weight baby (AOR 1.99, 95% CI: 1.00-3.98), all controlling for maternal age, race/ethnicity, marital status, education, health insurance status, income, and number of children in the household. Significant racial and ethnic disparities exist for pregnancy complications and non-live births, but not for low birth weight. Women's preconception mental health is a modifiable risk factor that stands to reduce the incidence of adverse pregnancy complications and birth outcomes.