Mean serum 25OHD concentration was 53.8 +/- 23.9 nmol/l (sd). Ln-25OHD was negatively correlated with serum parathyroid hormone as expected (r -0.24, confidence intervals -0.35 to -0.12). Ln-25OHD was also negatively correlated with fasting plasma glucose (r-0.20, -0.31 to -0.08), fasting insulin (r -0.20, -0.31 to -0.08) and insulin resistance as calculated by homeostasis model assessment (r -0.21, -0.32 to -0.09). The association between fasting glucose and log-transformed 25OHD concentration was of borderline significance after accounting for ethnicity, age and body mass index in multivariate analyses (-0.13, -0.26 to 0.01). The odds ratio of gestational diabetes in women with 25OHD < 50 nmol/l did not reach statistical significance (1.92, 95% confidence interval 0.89-4.17). CONCLUSIONS: Maternal 25OHD concentrations are inversely related to fasting glucose, although further studies are required to establish whether this is independent of the effects of ethnic background.