In this study, the authors compare perinatal health outcomes and nutrition risk assessments in Latina, African American, and white women receiving Medicaid enhanced perinatal services. The objective is to analyze how proper assessment of obesity and underweight depend upon ethnic group, provider practice setting and credentials, and the implications for perinatal outcomes. The medical records of women who received enhanced perinatal services from specially certified Medicaid providers in California were abstracted for information on nutrition risk assessment and outcomes. Logistic regression analysis was used to test the associations first of obesity and underweight with adverse outcomes in Latina, African American and white women, then the associations of ethnicity with the failure of these women to be classified as overweight or underweight during assessment. Finally, the associations between misclassification of body mass with provider practice setting type and credentials are also tested. Obese Latinas are twice as likely not to be properly classified as overweight, despite evidence of substantial risk of unfavorable outcomes. For all three ethnic groups, underweight women are uniformly underreported as being at risk. The appropriate classifications of obesity and underweight are not associated with private or public types of obstetric practice settings or whether nutrition risk assessors are registered dietitians, health workers, or nurses of any particular credential. Providers of prenatal care to low-income women could improve the quality of nutrition risk assessment of overweight Latina women and underweight women of all ethnic groups with expectations of improving perinatal outcomes.