Vitamin D supplementation may increase serum vitamin D levels in both mothers and infants (8, 9). However, what remains to be determined is whether vitamin D supplementation is protective against maternal morbid conditions, SGA, or intrauterine growth restriction, and whether it improves neonatal health. Findings from observational studies have been inconclusive, owing to the heterogeneity of the dose and duration of supplementation, the timing of supplementation initiation, maternal factors (overweight and obesity, general health before pregnancy), and measured endpoints.