[Seasonal variations in 25-hydroxycholecalciferol in cord blood of newborn infants].

An estimation of 25-hydroxycholecalciferol (25-OH-D3) by competitive proteic binding after silicic acid chromatography was performed in the cord blood of 130 neonates whose births were spaced throughout a whole year. The concentration of 25-OH-D3 is seen to rise regularly from May to August and then drops rapidly from September. The average value observed in the summer period (9,3 +/- 5,8 ng/ml) is worth twice the value of the cold season (4,7 +/- 1,7 ng/ml). A direct correlation can be seen ( y = 0,030 x + 1,68, r = 0,92, p less than 0,0001) between the average monthly rate (y: ng/ml) of 25-OH-D3 in the cord plasma and the number of sunny hours (x: hours/month) for the area concerned (Lyons, France) in the last month of pregnancy. This evidence suggests the possible existence of a relative vitamin D deficiency in the foetus and its possible cause as an aggravating feature in the hypocalcaemia of the neonate.