Association between the dietary inflammatory index and adverse pregnancy outcomes.

Background: Limited research exists on the association between preconception pro-inflammatory diets and adverse pregnancy outcomes, and this relationship remains poorly understood.

Objective: To investigate the association between preconception dietary inflammatory potential, as measured by the Dietary Inflammatory Index (DII), and adverse pregnancy outcomes in nulliparous individuals.

Methods: This was a secondary analysis of the data from the Nulliparous Outcomes Study: Mothers-to-be (nuMoM2b). Preconception dietary habits, assessed via food frequency questionnaires, were used to calculate DII scores based on 29 pro- and anti-inflammatory food items. Participants were categorized into DII quartiles (Q1-Q4), with Q1 representing the most anti-inflammatory and Q4 the most pro-inflammatory diets. The primary outcome was a composite of adverse pregnancy outcomes, including preterm birth, hypertensive disorders of pregnancy (preeclampsia, gestational hypertension, or eclampsia), small for gestational age (<5th percentile), and stillbirth. Secondary outcomes included the individual components of the primary outcome and gestational diabetes. Adjusted relative risks (aRR) and 95% confidence intervals (CIs) were calculated using modified Poisson regression, controlling for confounders.

Results: Among the 7,994 participants included, 1,829 (22.8%) experienced the primary outcome. Participants in Q4 had a significantly higher risk of the primary outcome compared to Q1 (25.9% vs. 22.1%; aRR 1.15, 95% CI 1.03-1.28) and a notably increased risk of stillbirth (0.9% vs. 0.3%; aRR 2.68, 95% CI 1.01-7.07). No significant associations were found for Q2 or Q3 compared to Q1 for the primary outcome (aRR 1.02, 95% CI 0.91-1.14; aRR 0.97, 95% CI 0.86-1.09, respectively). Other secondary outcomes were not statistically significant. Among individual food items, only folic acid was associated with a reduced risk of adverse pregnancy outcomes (aRR 0.97, 95% CI 0.94-0.99).

Conclusion: A pro-inflammatory preconception diet was associated with an increased risk of composite adverse pregnancy outcomes, particularly stillbirth, among nulliparous individuals. These findings underscore the potential role of dietary interventions during the preconception period to mitigate these risks.