Data are scarce regarding the prevalence and risk factors for antenatal suicidal ideation because systematic screening for suicidal ideation during pregnancy is rare. This study reports the prevalence and correlates of suicidal ideation during pregnancy. We performed cross-sectional analysis of data from an ongoing registry. Study participants were 2,159 women receiving prenatal care at a university obstetric clinic from January 2004 through March 2010. Multiple logistic regression identified factors associated with antenatal suicidal ideation as measured by the Patient Health Questionnaire. Overall, 2.7% of the sample reported antenatal suicidal ideation. Over 50% of women who reported antenatal suicidal ideation also reported major depression. In the fully adjusted model antenatal major depression (OR = 11.50; 95% CI 5.40, 24.48) and antenatal psychosocial stress (OR = 3.19; 95% CI 1.44, 7.05) were positively associated with an increased risk of antenatal suicidal ideation. We found that being non-Hispanic White was associated with a decreased risk of antenatal suicidal ideation (OR = 0.51; 95% CI 0.26–0.99). The prevalence of antenatal suicidal ideation in the present study was similar to rates reported in nationally representative non-pregnant samples. In other words, pregnancy is not a protective factor against suicidal ideation. Given the high comorbidity of antenatal suicidal ideation with major depression, efforts should be made to identify those women at risk for antenatal suicidal ideation through universal screening.