Relationship between the quality of the pregnant woman’s diet and birth weight: a prospective cohort study

Background Birth weight is a relevant predictor of childhood health outcomes. Studies investigating the association between modifiable risk factors, as the maternal diet quality, and birth weight are needed. We aimed to investigate the association between the Diet Quality Index Adapted for Pregnant Women (IQDAG) score and birth weight. Methods This is a prospective cohort that includes 547 Brazilian mother–child pairs. Dietary recalls and a food frequency questionnaire were obtained during pregnancy. Information on birth weight, sex, and gestation duration were obtained from the Live Birth Information System (SINASC). Results On total, 3.8% of the newborns were classified as low birth weight (LBW), 6.0% with macrosomia, 10.2% small for gestational age (SGA), and 11.2% large for gestational age (LGA). The mean (SD) IQDAG score was 70.1 (11.8). Adjusted logistic regression models showed that women in the third tertile of the IQDAG score presented a lower risk of having LGA babies [OR 0.44 (95% CI 0.22, 0.90), p-trend = 0.02] compared to the first tertile. Women in the third tertile of omega-3 intake presented a lower risk of giving birth to LGA infants [OR 0.33 (95% CI 0.15, 0.69), p-trend = 0.00] and LBW infants [OR 0.18 (95% CI 0.04, 0.83), p-trend = 0.02] when compared to the first tertile. There was also a lower SGA trend among the children of women in the third tertile of omega-3 intake [OR 0.43 (95% CI 0.17, 1.07), p-trend = 0.03] compared to the first tertile. Conclusion A better diet quality and higher omega-3 intake are protective factors for LGA babies, and increased maternal omega-3 intake reduce the risk of LBW and LGA, and may be a protective factor against the birth of SGA infants.