The incidence of hypocalcemia in newborn infant is greater in winter: 7.72% than in summer 2.63% if no vitamin D prophylaxis is given to the mother. After vitamin D supplementation, the incidence falls from 5.11 to 1.93%. This improvement occurs mainly in winter 7.72/2.43%. This last figure being equivalent in winter to the summer one above mentioned. Administration of a single dose (200,000 units vit D) at the end of pregnancy suppresses the seasonal handicap.