Serum levels of vitamin D metabolites, calcium, phosphorus, magnesium and alkaline phosphatase in Finnish women throughout pregnancy and in cord serum at delivery.

Serum concentrations of 25(OH)D, 24,25(OH)2D, 1,25(OH)2D, total calcium, protein, phosphorus, magnesium and alkaline phosphatase were measured in two groups of Finnish women throughout pregnancy and in cord serum at delivery. The autumn group delivered in August-September and the spring group in February-March. There was strong seasonal variation in the 25(OH)D concentrations in both groups. Maternal values (mean +/- s.d.) at delivery were 44.3 +/- 20.8 nmol/l in autumn and 26.0 +/- 13.0 nmol/l in spring. Fetal concentrations were 28.8 +/- 14.3 and 18.3 +/- 11.3 nmol/l, respectively. In both mothers and infants low 25(OH)D values were measured in winter. In the autumn group 7 out of 21 mothers (33 per cent) and in the spring group 17 out of 36 mothers (47 per cent) had values below 17 nmol/l, which is the lowest winter reference value recorded in our laboratory. No significant seasonal variation was observed in dihydroxylated vitamin D metabolites, although 24,25(OH)2D values were a little higher in summer than in winter. Concentrations of 1,25(OH)2D tended to rise towards delivery. Corrected calcium, magnesium and phosphorus concentrations did not change during pregnancy. Fetal calcium and phosphorus concentrations were significantly (P less than 0.001) higher than maternal ones. The data indicate that many mothers and infants have poor vitamin D status in the latitude of Finland. Our results support the concept that vitamin D supplementation should be considered in Finland for pregnant women at least in winter.