Dietary diversity as a modifier of the effect of supplementation with multiple micronutrients during pregnancy on low birth weight in a randomized controlled trial in Bangladesh.

BACKGROUND

Meta-analysis of trials of multiple micronutrient supplements (MMS) compared with iron-folic acid (IFA) suggests an overall benefit of 12% on low birth weight (LBW).

OBJECTIVES

Building on prior work showing that MMS is more effective in anemic and higher body mass index females; this paper explores whether dietary quality modifies the effect of MMS on birth weight.

METHODS

A 7-day food frequency questionnaire was administered in late pregnancy to 19,160 pregnant participants in the JiVitA-3 cluster-randomized controlled trial of MMS compared with IFA supplementation in Bangladesh. A 10-item dietary diversity score (DDS) was created by summing the number of food groups consumed ≥4 times per week. Risk ratios (RRs) and 95% confidence intervals (CIs) for the effect of MMS compared with IFA on LBW were estimated by DDS. The interaction between DDS and MMS was tested using a generalized estimating equations log-binomial regression model to account for the cluster randomization. Point estimates and 95% CI for the effect of MMS on LBW were estimated at each DDS. Models were adjusted for confounders. We used P < 0.1 to determine the statistical significance of the interaction.

RESULTS

The median DDS was 3 (interquartile range: 2, 4), and 18.6% of pregnant women had a score ≥ 5. The fully adjusted protective effect of MMS on LBW was inversely associated with dietary diversity [MMS×DDS RR: 1.02 (95% CI: 1.00, 1.04), P-interaction = 0.05]. The effect was greatest at the lowest DDS [DDS= 1, RR LBW: 0.86 (0.81, 0.91)] and decreased at higher scores [DDS = 7, RR: 0.92 (0.84, 1.00)].

CONCLUSIONS

In rural Bangladesh, where maternal dietary diversity was generally low, MMS (compared with IFA) supplementation had the strongest effect on reducing low birth weight among pregnant females with the least diverse diet, possibly reflecting the additional benefit of supplementation in this vulnerable group. This trial was registered at clinicaltrials.gov as NCT00860470.