Does the effect of micronutrient supplementation on neonatal survival vary with respect to the percentiles of the birth weight distribution

Scientic Background: In developing countries, higher infant mortality is partially caused by poor maternal and fetal nutrition. Clinical trials of micronutrient supplementation are aimed at reducing the risk of infant mortality by increasing birth weight. Because infant mortality is greatest among the low birth weight infants (LBW) ( 2500 grams), an eectiv e intervention may need to increase birth weight among the smallest babies. Although it has been demonstrated that supplementation increases the birth weight in a trial conducted in Nepal, there is inconclusive evidence that the supplementation improves their survival. It has been hypothesized that a potential benet of the treatment on survival among the LBW infants is partly compensated by a null or even harmful eect among the largest infants. Exploratory analyses have suggested that the treatment eect on birth weight might vary with respect to the percentiles of the birth weight distribution. Data: The methods in this paper are motivated by a double-blind randomized community trial in rural Nepal (Christian et al 2003a,b). The investigators implemented an intervention program to evaluate benets of the following micronutrient supplementations: folic acid and vitamin A (F+A); folic acid, iron, and vitamin A (F+I+A); folic acid, iron, zinc, and vitamin A (F+I+Z+A); multiple nutrients and vitamin A (M+A). Each micronutrient supplement was administered daily to 1000 pregnant women, who ultimately delivered approximately 800 live-born infants. The team measured the birth weight within 72 hours of delivery and then followed the infants for one year to determine whether or not they survived. In addition, they measured several characteristics of the mother (maternal age, maternal height, arm circumference) and of the infant (weight, length, head and chest circumference).