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Summary

Objective  Vitamin D is essential for skeletal health and prolonged deficiency results in infantile rickets and adult osteomalacia. The aim of this study is to determine the vitamin D status in pregnancy and to evaluate the effects of daily and of single-dose vitamin D supplementation.

Design  A prospective randomized study at St Mary's Hospital London.

Patients A total of 180 women (Indian Asian, Middle Eastern, Black and Caucasian) were recruited at 27 weeks gestation and randomized into three treatment groups: a single oral dose of 200 000 IU vitamin D, a daily supplement of 800 IU vitamin D from 27 weeks until delivery and a no treatment group.

Measurements  Vitamin D (25-hydroxyvitamin D), PTH and corrected calcium levels in mothers at 27 weeks and at delivery and cord 25-hydroxyvitamin D and corrected calcium levels.

Results  The final maternal 25-hydroxyvitamin D levels were significantly higher in the supplemented group [daily dose (median) 42 (IQR 31–76) nmol/l, stat dose (median) 34 (IQR 30–46) nmol/l vs. median 27 (IQR 27–39) nmol/l in the no treatment; P < 0·0001] and significantly fewer women with secondary hyperparathyroidism in the supplemented group (10% in daily dose vs. 12% in stat dose vs. 27% in the no treatment; P < 0·05). Cord 25-hydroxyvitamin D levels were significantly higher with supplementation [daily dose median 26 (IQR 17–45) nmol/l, stat dose median 25 (IQR 18–34) nmol/l vs. median 17 (IQR 14–22) nmol/l in no treatment; P = 0·001].

Conclusion  Single or daily dose improved 25-hydroxyvitamin D levels significantly. However, even with supplementation, only a small percentage of women and babies were vitamin D sufficient. Further research is required to determine the optimal timing and dosing of vitamin D in pregnancy.