Background: Accumulating evidence indicates that maternal diets are important for optimizing maternal and offspring health. Existing research lacks comprehensive profiles of maternal diets throughout pregnancy, especially in a racially/ethnically diverse obstetrical population. Objective: The aim was to characterize diets in a longitudinal US pregnancy cohort by trimester, race/ethnicity, and prepregnancy BMI. Methods: Data were obtained from pregnant women in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies-Singleton cohort (2009-2013). A food-frequency questionnaire (FFQ) at 8-13 wk of gestation assessed periconception and first-Trimester diet (n = 1615). Automated, self-Administered, 24-h dietary recalls targeted at 16-22, 24-29, 30-33, and 34-37 wk of gestation assessed second-and third-Trimester diets (n = 1817 women/6791 recalls). The Healthy Eating Index-2010 (HEI-2010) assessed diet quality (i.e., adherence to US Dietary Guidelines). Variations in weighted energy-Adjusted means for foods and nutrients were examined by trimester, self-identified race/ethnicity, and self-reported prepregnancy BMI. Results: Mean (95% CI) HEI-2010 was 65.9 (64.9, 67.0) during periconception to the first trimester assessed with an FFQ and 51.6 (50.8, 52.4) and 51.5 (50.7, 52.3) during the second trimester and third trimester, respectively, assessed using 24-h recalls. No significant differences were observed between the second and third trimester in macronutrients, micronutrients, foods, or HEI-2010 components (P ≥ 0.05). Periconception to first-Trimester HEI-2010 was highest among Asian/Pacific Islander [67.2 (65.9, 68.6)] and lowest among non-Hispanic Black [58.7 (57.5, 60.0)] women and highest among women with normal weight [67.2 (66.1, 68.4)] and lowest among women with obesity [63.5 (62.1, 64.9)]. Similar rankings were observed in the second/third trimesters. Conclusions: Most pregnant women in this cohort reported dietary intakes that, on average, did not meet US Dietary Guidelines for nonpregnant individuals. Also, diet differed across race/ethnic groups and by prepregnancy BMI, with the lowest overall dietary quality in all trimesters among non-Hispanic Black women and women with obesity. No meaningful changes in dietary intake were observed between the second and third trimesters.