USE OF VITAMIN D IN PREGNANCY

Vitamin D encompasses a large family of fat-soluble steroid preprohormones. Humans require vitamin D2 (ergocalciferol), present in some foods such as fungi, and vitamin D3 (colecalciferol), which is synthesised in the skin and present in oily fish/cod liver oil. In the UK vitamin D deficiency is defined as calcifediol (25(OH)D) <25nmol/l. 

Vitamin D deficiency in pregnancy may be associated with an increased risk of small for gestational age infants, preterm delivery, infantile rickets and maternal pre-eclampsia. 

Routine supplementation: Vitamin D supplements of 400IU (10µg)/day vitamin D (or equivalent) are currently recommended for all pregnant and breastfeeding women. There is no evidence from epidemiological studies that use of the above dose of vitamin D, or any of its analogues, is associated with an increased risk of congenital malformation, however data are limited. There are insufficient data to determine whether there are any associations between maternal vitamin D supplementation during pregnancy and the risk of miscarriage. Vitamin D supplementation is not associated with an increased risk of preterm delivery, small for gestational age, low birth weight, intrauterine or neonatal death.

Treatment of deficiency: There are insufficient data to provide recommendations regarding high dose vitamin D for established vitamin D deficiency in pregnancy. RCOG Scientific Impact Paper recommends the treatment of vitamin D-deficient pregnant women with either colecalciferol 20,000IU/week or ergocalciferol 10,000IU twice a week for 4–6 weeks. No adverse outcomes were identified in a small case series of pregnant women with hypoparathyroidism treated with vitamin D2 doses up to 6.25mg (250,000IU) per day. Whilst reassuring, due to the small study population size, these data are considered too limited to exclude the possibility of risk.

Treatment with very high doses of vitamin D may induce hypercalcaemic vitamin D toxicity, although this is usually associated with serum calcifediol levels in excess of 350nmol/l. Regular monitoring of plasma calcium concentration is advised for all pregnant patients receiving high doses of vitamin D.

Use of vitamin D or vitamin D analogues (present in dietary supplementation products) taken at the recommended dose do not require additional fetal monitoring. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Where exposure to larger doses has occurred, discussion with UKTIS is recommended.