Original Article Vitamin D testing in pregnancy: Does one size fit all? Miranda DAVIES-TUCK, 1,2 Cheryl YIM, 3 Michelle KNIGHT, 3 Ryan HODGES, 2 James C.G. DOERY 4 and Euan WALLACE 1,2,3 1 The Ritchie Centre, MIMR-PHI Institute of Medical Research, 2 Department of Obstetrics and Gynaecology, School of Clinical Sciences, Monash University, 3 Monash Women’s Maternity Services, Monash Health, Monash Medical Centre and 4 Monash Pathology Australia, Monash Health, Monash Medical Centre, Clayton, Vic., Australia 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. Key words: pregnancy, pregnancy outcomes, vitamin D. Introduction Over the past decade, the role of vitamin D and vitamin D deficiency in health and disease has emerged as an issue of considerable public health interest. 1 Even in countries with high levels of sunlight, such as Australia, between a quarter to a third of adults are vitamin D deficient, as determined by accepted vitamin D normal ranges. 2 It is not surprising then that vitamin D deficiency in pregnant women is common. 3 This may be important because there is a growing number of reports linking vitamin D deficiency during pregnancy with several adverse pregnancy outcomes, including increased risks of gestational diabetes (GDM), pre-eclampsia (PE), low birthweight, preterm birth, caesarean section and postpartum depression, 4,5 although the reports are not consistent. 3,7 It has also been suggested that maternal vitamin D 6 deficiency may contribute to various childhood diseases in the offspring beyond the well-recognised risks of low bone mineral density and rickets. For example, there are reports that low vitamin D status in pregnancy is associated with child- hood asthma, diabetes, eczema, impaired psychomotor development and learning, and schizophrenia. 8–12 However, the associations are not consistent, and studies are often limited by methodological flaws 3,13 such that the evidence that maternal vitamin D status contributes to these adverse pregnancy outcomes remains inconclusive. Further, even if vitamin D deficiency does contribute to suboptimal outcomes, it is unclear what level of vitamin D confers optimal outcomes and, as a consequence, what supplementation is required to achieve and maintain adequate vitamin D levels. 14 For example, a recent consensus expert opinion suggested that a vitamin D concentration <50 nmol/L represented deficiency and Correspondence: Dr Miranda Davies-Tuck, The Ritchie Centre, MIMR-PH Institute of Medical Research, Monash Medical Centre, Clayton, Vic. 3168, Australia. Email: miranda.davies@monash.edu Received 19 June 2014; accepted 20 September 2014. © 2015 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists 149 Australian and New Zealand Journal of Obstetrics and Gynaecology 2015; 55: 149–155 DOI: 10.1111/ajo.12278 Te Australian and New Zealand Journal of Obstetrics and Gynaecology