Type of publicationArticle (peer-reviewed)Link to publisher's version http://dx.doi.org/10.1017/S0007114516003202Access to the full text of the published version may require a subscription. Rights © The Authors 2016Embargo information Access to this article is restricted until 12 months after publication by the request of the publisher Abstract Vitamin D insufficiency and deficiency have been associated with an increased risk of adverse pregnancy outcomes. Controversy remains as findings have been inconsistent between disparate populations. The aim of this study was to investigate the relationship between vitamin D status and pregnancy outcomes in a large, prospective pregnancy cohort. 25-Hydroxyvitamin D concentration was analysed in serum samples collected at 15 weeks of gestation from 1710 New Zealand women participating in a large, observational study. Associations between vitamin D status and pre-eclampsia, preterm birth, small for gestational age (SGA) and gestational diabetes were investigated. The mean 25-hydroxyvitamin D concentration was 72·9 nmol/l. In all, 23 % had 25-hydroxyvitamin D concentrations <50 nmol/l, and 5 % of participants had concentrations <25 nmol/l. Women with 25-hydroxyvitamin D concentrations <75 nmol/l at 15 weeks of gestation were more likely to develop gestational diabetes mellitus than those with concentrations >75 nmol/l (OR 2·3; 95 % CI 1·1, 5·1). However, this effect was not significant when adjustments were made for BMI and ethnicity (OR 1·8; 95 % CI 0·8, 4·2). 25-Hydroxyvitamin D concentration at 15 weeks was not associated with development of pre-eclampsia, spontaneous preterm birth or SGA infants. Pregnancy complications were low in this largely vitamin D-replete population.Key words: Vitamin D: Gestational diabetes mellitus: Pre-eclampsia Much progress has been made in the screening, diagnosis and management of important pregnancy disorders, but little progress has been made in the prevention of such disorders. Preeclampsia remains the second most common cause of maternal death worldwide (1) . Prematurity, mostly due to spontaneous preterm birth, is the leading cause of death among infants worldwide (2) . This is followed by growth restriction in term infants (3) . Furthermore, infants born preterm or with low birth weight have an increased risk of CVD and metabolic diseases later in life, the leading cause of death in adulthood (4) . The incidence of gestational diabetes mellitus (GDM) is increasing rapidly worldwide (5) and is associated with lifelong risks of metabolic disease in both mother and baby (6,7) . An association between low vitamin D and adverse pregnancy outcomes was first identified in the early 2000s (8) ; consequently, vitamin D has been postulated as a possible intervention strategy to reduce pregnancy complications. A recent meta-analysis found that low vitamin D, defined variably by the authors of included studies, was associated with an increased likelihood of pre-eclampsia (OR 1·79; 95 % CI 1·25, 2·58), small-for-gestational age (SGA) babies (OR 1·...

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