Seasonal variation in serum-25-OH-D3 in mothers and newborn infants in northern finland.

Two groups, each consisting of twenty Finnish mother-neonate pairs and ten non-pregnant controls were studied for serum calcium, serum phosphate, serum alkaline phosphatase, parathormone index (PTHind) and S-25-OH-D3. The first series was collected in winter and the other in summer. The serum samples were taken on the third day after delivery. The concentrations of S-25-OH-D3 were significantly lower in the mothers than in the non-pregnant controls in winter, but the difference was not significant in summer. The concentrations of S-25-OH-D3 in the serum of the mothers were similarly significantly lower in winter than in summer, ten mothers exhibiting a value below the detection line in winter, but only two in summer. The concentrations of S-25-OH-D3 in the mothers and their newborn infants showed a close relationship, but when extremely low values existed in the mothers, the infant concentrations were slightly higher. The seasonal variation in S-25-OH-D3 was also significant in the neonates. Although calcium was decreased and alkaline phosphatase elevated when compared with the non-pregnant controls in the mothers in both groups, these values showed no seasonal variation, and the mean levels of serum calcium, phosphate, alkaline phosphatase and PTHind in the neonates also remained unaltered between the two groups. The results indicate that additional vitamin D should be supplied during pregnancy in the winter months at this latitude.