Study seem to have addressed point #2 in several ways. 1. They measured maternal vitamin D before supplementation began. They explicitly adjusted for these pr

Study seem to have addressed point #2 in several ways. 1. They measured maternal vitamin D before supplementation began. They explicitly adjusted for these preintervention levels. 2. the two groups started at essentially the same vitamin D levels. 3. They specifically tested whether baseline vit D status changed the effect of supplementation