Parker HW, et al. - Researchers performed this secondary analysis to determine the association between gestational weight gain, prepregnancy BMI, and prenatal diet quality in a United States national sample. From the longitudinal Infant Feeding Practices Study II, 1,322 pregnant women with Diet History Questionnaire data were assessed. Using the Alternative Healthy Eating Index for Pregnancy, assessment of diet quality in the third trimester was done. Adherence to the Institute of Medicine’s recommendations was categorized as inadequate, adequate, or excessive weight gain based on self-reported prepregnancy BMI (categorized as underweight < 18.5, normal weight 18.5–24.9, overweight 25.0–29.9, and obese ≥ 30.0) and total gestational weight gain. The analysis revealed an inverse correlation of both prepregnancy BMI and gestational weight gain with diet quality scores. As prepregnancy BMI significantly interacted with gestational weight gain, they stratified gestational weight gain models by BMI group. In stratified adjusted models, women with underweight, normal weight, overweight, and obesity exhibited differences in the association between gestational weight gain and diet quality scores. Prepregnancy BMI seemed influencing the relationship between gestational weight gain and prenatal diet quality. For instance, within women with normal weight, they observed higher diet quality in the adequate gestational weight gain group. Findings emphasize the necessity for interventions to broadly improve prenatal diet quality, however, resources can be employed to target women with higher prepregnancy BMIs and women with inadequate or excessive gestational weight gain.