Vitamin D metabolism in normal and hypoparathyroid pregnancy and lactation

Plasma concentrations of vitamin D metabolites in 17 non-pregnant women, 22 pregnant women at delivery, and in eight lactating women 3 and 16 days after delivery, were compared with those in a postpartum hypoparathyroid patient treated with 1 alpha-hydroxyvitamin D (1 alpha-OHD). The mean concentration of 1,25-dihydroxyvitamin D [1,25-(OH)2 D] was 203 (SD 61) pmol/l in the pregnant, and 86 (SD 27) pmol/l in the non-pregnant women (P less than 0.0005). The levels 3 and 16 days after delivery were similar [57 (11) compared with 62 (19) pmol/l], and lower than the non-pregnant value (P less than 0.01). The 25-hydroxyvitamin D (25-OHD) concentration remained unchanged between the 3rd and 16th days after delivery, whereas the 24,25-dihydroxyvitamin D [24,25-(OH)2D] level increased from 2.7 (SD 1.8) to 3.7 (SD 2.3) nmol/l (P less than 0.025). The patient temporarily required an increased supplement of l alpha-OHD during pregnancy, but a dose which was appropriate before pregnancy resulted in marked hypercalcaemia and a rise of 1,25-(OH)2D concentration within 16 days of delivery despite lactation. The results suggest that the metabolic need for the active vitamin D metabolite 1,25-(OH)2D is increased during pregnancy and rapidly reduced during early lactation in healthy and hypoparathyroid women.