BackgroundAlthough diet quality during pregnancy and postpartum is important for multiple parent and child outcomes, within-person changes in diet quality throughout these periods have not been extensively examined. ObjectivesThis study investigated diet quality from early pregnancy through 1 y postpartum and examined differences by sociodemographic characteristics in participants receiving obstetric care in Chapel Hill, North Carolina, United States. MethodsParticipants completed 24-h dietary recalls at 6 study visits (each pregnancy trimester and 6 wk, 6 mo, and 1 y postpartum) (n = 383). Between-visit mean Healthy Eating Index-2015 (HEI) scores (min = 0, max = 100) were compared using the population ratio (PR) method. The NCI usual intakes method estimated the distribution of HEI scores in pregnancy and postpartum; unpaired t-tests compared usual mean HEI scores by covariates; paired t-tests compared differences between mean pregnancy and postpartum. ResultsThe total HEI mean ± standard error scores (NCI method) were 61.4 ± 0.8 in pregnancy and 61.7 ± 0.9 in postpartum. Mean HEI scores differed by sociodemographic characteristics, particularly education, marital status, and federal assistance participation. The highest scores were observed in participants with at least a bachelor’s degree (64.1 ± 0.9 in pregnancy, 64.5 ± 1.0 in postpartum, n = 257) and those with other non-Hispanic White race/ethnicity (64.7 ± 1.8 in pregnancy, 66.4 ± 2.2 in postpartum). There were no between-visit differences in mean total HEI scores (PR). Although differences were observed in some mean HEI component scores between pregnancy and postpartum visits, they were small (mostly <1 point) in magnitude and in inconsistent directions. ConclusionsStable total HEI mean scores suggest that adherence to dietary guidelines was consistent throughout pregnancy and postpartum in this sample. Although some sociodemographic characteristics may identify individuals at greater risk of diet-related pregnancy complications, low diet quality was pervasive throughout all subgroups and reflects an urgent need for widespread improvement.