Vitamin D testing in pregnancy: Does one size fit all?

BACKGROUND: Vitamin D deficiency is common. What the optimum level of vitamin D in pregnancy and whether vitamin D supplementation in pregnancy confers improved health benefits remain controversial. AIM: To assess vitamin D status in pregnant women in a maternity service that recommends routine antenatal screening and advises supplementation where necessary, and to assess relationships between early pregnancy vitamin D levels and changes in vitamin D across pregnancy with pregnancy outcomes. MATERIALS AND METHODS: Vitamin D serum concentrations were measured in early and late pregnancy. The relationships between initial vitamin D status, maternal factors and pregnancy outcomes were estimated. Change in vitamin D over pregnancy was quantified. The relationship between change in vitamin D over pregnancy and pregnancy outcomes was also estimated. RESULTS: Of 1550 women, 849 (55%) were vitamin D deficient (<50 nmol/L), 571 (37%) were insufficient (50-74 nmol/L), and 130 (8%) were replete (≥75 nmol/L) in early pregnancy. Factors associated with deficiency were increased body mass index, pregnancy in either winter or spring months, and maternal country of birth (South-East, South and East Asia, and Africa). Vitamin D deficiency or insufficiency in early pregnancy was significantly associated with developing gestation diabetes mellitus. Levels of vitamin D significantly increased over pregnancy among nonreplete women. Increasing vitamin D over pregnancy was not related to pregnancy outcomes. CONCLUSION: Vitamin D 'deficiency' is common but may not be associated with most adverse pregnancy outcomes. Routine vitamin D testing of all pregnant women does not appear warranted.