Endocrine Abstracts

Vitamin D deficiency is more common in pregnant women than in non-pregnant women of similar age. Clinical vitamin D deficiency, associated with rickets and osteomalacia, may occur when serum 25-hydroxyvitamin D (25(OH)D) is lower than 25 nmol/l. The required serum 25(OH)D is currently set at 50 nmol/l, as lower levels are associated with lower bone mineral density, increased fracture risk and other outcomes such as lower physical performance than a vitamin D adequate state, i.e. serum 25(OH)D above 50 nmol/l. Many studies show low serum levels of 25-hydroxyvitamin D (25(OH)D) in pregnant women and in their offspring. Serum 25(OH)D is about 20% lower in the neonate (cord blood) than in the mother. During normal pregnancy, the concentration of the active metabolite 1,25-dihydroxyvitamin D (1,25(OH)2D) increases in the first trimester, due to the increase of the vitamin D binding protein. The free concentration of 1,25(OH)2D increases in the third trimester when the daily transfer of calcium through the placenta increases to more than 300 mg/day. Vitamin D defiency in the mother is associated with a higher risk of pre-eclampsia and gestational diabetes. Severe vitamin D deficiency in the mother can lead to neonatal hypocalcemia and tetany, low birth weight and rickets. Vitamin D deficiency in the mother is also associated with astma in the child, with lower bone mineral density in the first year and at 9 years of age. The most important risk group for vitamin D deficiency in pregnancy are non-western immigrants. A survey in The Hague in the Netherlands showed very low mean serum 25(OH)D levels in Turkish and Moroccan women (15.2±12.1 and 20.1±13.5 nmol/l respectively), and 25(OH)D was not detectable in 22% of the Turkish women.

The most recent guideline of the Institute of Medicine (2011) concluded that the required serum 25(OH)D level meeting the needs of 97.5% of the population is 50 nmol/l. The recommended dietary allowance for pregnant women is 600 IU/day. However, many uncertainties remain regarding the consequences of vitamin D deficiency in pregnancy. There is a lack of double blind randomized trials in pregnant women with sufficiently long follow-up to determine the effects of vitamin D supplementation in mother and child.