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

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.