Dietary Fat and Fatty Acid Intake in Nulliparous Women: Associations with Preterm Birth and Distinctions by Maternal BMI

Abstract

ABSTRACT Background Evidence documenting whether diet quality, particularly dietary fatty acids, is associated with preterm birth (PTB) is limited. Objective The aim was to measure associations between dietary fatty acid intake prior to pregnancy, specifically n–3 (ɷ-3) PUFAs and odds of PTB in US women and determine if associations differed by prepregnancy BMI. Methods We designed a secondary analysis of dietary intake in nulliparous women enrolled in a longitudinal cohort (NCT01322529). Participants completed an FFQ, modified to assess detailed PUFA intake, during the 3 mo preceding pregnancy. Inclusion in this analytic cohort required total energy intake within 2 SDs of the group mean. Prepregnancy BMI was categorized as underweight, normal, overweight, or obese. The primary exposure was estimated intake of EPA and DHA (combined EPA+DHA), in the context of a recommended intake of 250 mg. The primary outcome was PTB (<37 wk). Adjusted regression models controlled for maternal factors relevant to PTB and evaluated associations with PUFAs. Interaction terms estimated effect modification of BMI. A false discovery rate (FDR) correction accounted for multiple comparisons. Results Median daily intake of combined EPA+DHA in 7365 women was 70 mg (IQR: 32, 145 mg). A significant interaction term indicated the effects of EPA+DHA on odds of PTB were different for different BMI categories (P < 0.01). Specifically, higher intake of combined EPA+DHA was nominally associated with reduced odds of PTB in women with underweight (OR: 0.67; 95% CI: 0.46–0.98) and normal BMI (OR: 0.87; 95% CI: 0.78–0.96), yet was associated with increased odds of overweight BMI (OR: 1.21; 95% CI: 1.02–1.44). Associations remained significant after FDR correction. Conclusions Based on a cohort of US women designed to identify predictors of adverse pregnancy outcomes, dietary intake of combined EPA+DHA was considerably lower than recommended. Associations between intake of these recommended n–3 fatty acids and risk of PTB differ by maternal BMI.