Dietary Intake. Participants were asked to complete a dietary recall within each study visit window using the Automated Self-Administered 24-Hour Recall (ASA24), a web-based tool for obtaining self-administered 24-hour dietary recalls developed by the National Cancer Institute and validated against the interviewer-administered automated multiple pass method (40, 41). The ASA24 prompts participants to indicate all foods consumed, including details of food preparation, brands, portion size, and additions. From this data, the program assigns food codes from the U.S. Department of Agriculture Food and Nutrient Database for Dietary Surveys and provide estimates of macronutrient, micronutrient, food categories and USDA Food Patterns Equivalents Database food groups. Participants received written instructions on use of the program, and research staff provided assistance if participants reported difficulty using the interface. Research staff at the University of North Carolina Nutrition and Obesity Research Core identified and corrected implausible entries (e.g., food items with implausible energy, fat or weight) and missing food or nutrient values and quantities. Dietary records indicating daily energy intakes of < 600 kcal (36 of 1883 records, 1.9%) were excluded from analyses. Dietary records with daily energy intakes of > 4500 kcal were reviewed and determined to reflect plausible intake. Dietary intake data were used to calculate the Healthy Eating Index-2015 (HEI), an a priori indicator of diet quality that reflects conformance to the 2015 US Dietary Guidelines for Americans (42). The HEI total score ranges from 0–100 and is calculated by summing 13 component scores, including 9 “adequacy components” (total fruit, whole fruit, total vegetables, greens and beans, whole grains, dairy, total protein, seafood and plant proteins, fatty acids) and 4 “moderation components” (refined grains, sodium and added sugars and saturated fats), which are calculated on a per-1000 kcal or percent of kcal basis. Subscale scores reflecting adherence to adequacy (max score = 60) and moderation (max score = 40) components were also calculated. Diet recalls from pregnancy and those from postpartum were combined to calculate HEI across pregnancy (n = 365) and across postpartum (n = 266).
Hedonic Hunger. The Power of Food Scale (PFS) is a 15-item questionnaire that measures hedonic hunger, the appetitive response to highly-palatable food cues in the environment (43). Items querying response to the availability, presence, or taste of desirable food are rated on a 5-point Likert scale. The measure demonstrates strong internal consistency (Cronbach’s alpha = 0.91) and test-retest reliability (r = 0.77, p < 0.001), and has been validated with respect to overeating (29), outcomes of weight-loss interventions (44), and brain activity in response to viewing images of food versus control (45). The PFS was completed each trimester during pregnancy and at 6 months postpartum (n = 227); mean scores across pregnancy were calculated (n = 377).
Addictive-like Eating. The modified Yale Food Addiction Scale (mYFAS), a 9-item abbreviated version (46) of the Yale Food Addiction Scale assesses the presence of eating disorder symptoms consistent with diagnostic criteria for food addiction. The measure has demonstrated psychometric properties similar to the original instrument, and greater scores were associated with higher BMI across two cohorts of women (46). The mYFAS was completed at baseline (n = 344) and 6-months postpartum (n = 217). Due to the highly skewed distribution, responses of 2 or more (12.5% of responses) were collapsed (only 2.3% of respondents scored 3 and 1.8 scored 4 or higher).
Food Reinforcement Measures. The Food Reinforcement Questionnaire (FRQ) (47) and Multiple Choice Procedure (MCP) (48) assessed the relative reinforcing value of food. The FRQ asks participants to report the number of portions of a specified food that they would purchase for same-day intake at varying cost levels. The measure generates five indices: breakpoint (first price at which consumption was zero), intensity of demand (consumption at the lowest price), elasticity of demand (sensitivity of consumption to increase in cost; individual elasticities calculated using the modified exponential demand equation) (49), Omax (maximum expenditure), and Pmax (price at which expenditure was maximized). The measure has demonstrated validity against a laboratory task assessing food reinforcement value (47). The MCP asks participants to make a series of discrete choices between receiving an increasing amount of a monetary reward versus an alternative reinforcer. The datum of interest is the specific price at which participants begin to select the money over the reinforcer (breakpoint). The MCP has previously been validated in the assessment of reinforcement value of alcohol and cigarettes (e.g., 50), and was adapted by the investigators to assess the relative reinforcing value of food. Subjects were presented with the name and images of 18 palatable foods and asked to provide hedonic ratings. The two highest-rated foods were then used for the FRQ and MCP, which were assessed at the first two pregnancy visits and six months postpartum (n = 209 for FRQ and 211 for MCP). For each measure, mean scores across the two pregnancy visits were calculated (n = 348 for FRQ and 350 for MCP). Due to highly skewed distributions, scores were grouped into quartiles for analysis.
Self-control. Two measures of self-control were administered. The 15-item short form of the Barratt Impulsiveness Scale (BIS-15) measures impulsivity across three dimensions – non-planning, motor impulsivity, and attentional impulsivity. The measure has demonstrated similar psychometric properties and associations with neurobehavioral traits as the original instrument (51). The Delaying Gratification Inventory (DGI) is a 35-item questionnaire measuring the tendency to forego immediate satisfaction in favor of long-term rewards across five domains – food, physical pleasure, social interaction, money and achievement (52). The subscale scores have shown good internal consistency (Cronbach’s alpha = 0.69–0.89) and strong test-retest reliability (r = 0.74–0.90). Both measures were completed at baseline (n = 314 for BIS and 330 for DGI) and 6 months postpartum (n = 215 for BIS and 219 for DGI). For this study, associations with the total score and the food subscale (DGI-food) were examined.
Home Food Environment. The Home Food Inventory includes a comprehensive range of foods in 15 categories and queries the presence of each food in the home (53). Participants completed the inventory at baseline (n = 303) and 6 months postpartum (n = 266). Consistent with the measure’s scoring protocol, a fruit and vegetable home food environment score (HFI-FV) and an obesogenic home food environment score (HFI-OBES) were calculated as counts of the number of foods in the home in each classification. The fruit and vegetable score includes 26 common fruits and 20 common vegetables. Foods classified as obesogenic include regular-fat versions of cheese, milk, yogurt, other dairy, frozen desserts, prepared desserts, savory snacks, added fats, regular-sugar beverages, processed meat, high-fat microwavable foods, candy, and access to unhealthy foods in refrigerator and kitchen.
Demographic and medical characteristics. Demographic information including household composition, marital status, education, and race/ethnicity were reported by participants at baseline. Income-to-poverty ratio was calculated from family income and household size (54); higher values indicate greater income relative to the poverty threshold. Participant age and parity were obtained from the electronic medical record.