Better Diet Quality during Pregnancy Is Associated with a Reduced Likelihood of an Infant Born Small for Gestational Age: An Analysis of the Prospective New Hampshire Birth Cohort Study.

Background: Birth weight has a U-shaped relation with chronic disease. Diet quality during pregnancy may impact fetal growth and infant birth weight, yet findings are inconclusive. Objective: We examined the relation between maternal diet quality during pregnancy and infant birth size among women enrolled in a prospective birth cohort. Methods: Women 18-45 y old with a singleton pregnancy were recruited at 24-28 wk of gestation from prenatal clinics in New Hampshire. Women completed a validated food frequency questionnaire at enrollment. Diet quality was computed as adherence to the Alternative Healthy Eating Index. Infant birth outcomes (sex, head circumference, weight, and length) were extracted from medical records. Weight-for-length z scores, low birth weight, macrosomia, and size for gestational age [small for gestational age (SGA) or large for gestational age (LGA)] were computed. Multivariable regression models fit each outcome on quartiles of diet quality, adjusted for covariates. Models were computed overall and stratified by smoking status. Results: Analyses included 862 women and infants with complete data. Lower diet quality was associated with lower maternal education, being a smoker, prepregnancy obesity status, and lack of exercise during pregnancy. Overall, 3.4% of infants were born with a low birth weight, 12.1% with macrosomia, 4.6% were SGA, and 8.7% were LGA. In an adjusted model, increased diet quality appeared linearly associated with a reduced likelihood of SGA (P-trend = 0.03), although each quartile comparison did not reach statistical significance. Specifically, ORs for SGA were 0.89 (95% CI: 0.37, 2.15), 0.73 (95% CI: 0.28, 1.89), and 0.35 (95% CI: 0.11, 1.08) for each increasing quartile of diet quality compared to the lowest quartile. Similar trends for SGA were observed among non-smokers (n = 756; P-trend = 0.07). Also among non-smokers, increased diet quality was associated with lower infant birth weight (P-trend = 0.03) and a suggested reduction in macrosomia (P-trend = 0.07). Conclusions: Increased diet quality during pregnancy was related to a reduced risk of SGA in this cohort of pregnant women from New Hampshire. Additional studies are needed to elucidate the relation between maternal diet quality and macrosomia.