To test the hypothesis that maternal food fortification with omega-3 fattyacids and multiple micronutrients increases birth weight and gestationduration, as primary outcomes.

Non-blinded, randomised controlled study.

Pregnant women received powdered milk during their health check-ups at 19antenatal clinics and delivered at two maternity hospitals in Santiago,Chile.

Pregnant women were assigned to receive regular powdered milk (n = 477) or a milk product fortified withmultiple micronutrients and omega-3 fatty acids (n = 495).

Intention-to-treat analysis showed that mean birth weight was higher in theintervention group than in controls (65.4 g difference, 95% confidenceinterval (CI) 5–126 g; P =0.03) and the incidence of very preterm birth (<34 weeks) waslower (0.4% vs. 2.1%; P = 0.03).On-treatment analysis showed a mean birth weight difference of 118 g (95% CI47–190 g; P = 0.001) and arelative fall in both the proportion of birth weight ≤3000 g(P = 0.015) and the incidence ofpre-eclampsia (P = 0.015). Compliancewith the experimental product was apparent from a haematological study ofred-blood-cell folate at the end of pregnancy, which was performed in asub-sample. In both types of analyses, positive differences were alsopresent for mean gestation duration, birth length and head circumference.Nevertheless, the relatively small sample sizes allowed a statistical powerof >0.80 just for mean birth weight and birth length in theon-treatment analysis; birth length in that analysis had a difference of0.57 cm (95% CI 0.19–0.96 cm; P = 0.003).

The new intervention resulted in increased mean birth weight. Associationswith gestation duration and most secondary outcomes need a larger samplesize for confirmation.