Early-pregnancy maternal vitamin D status and maternal hyperglycaemia

Aims To estimate the association between serum 25-hydroxyvitamin D concentrations and maternal hyperglycaemia (post-load glucose concentration 7.5mmol/l). Methods Pregnant women (n=429; 61% black, 36% obese, 45% smokers) enrolled in a cohort study at <16weeks gestation. Non-fasting blood samples were assayed for serum 25-hydroxyvitamin D at enrolment. At 24-28weeks gestation, maternal hyperglycaemia was determined using a 50-g 1-h oral glucose challenge test. Results A total of 67% of women had 25-hydroxyvitamin D concentrations < 50nmol/l and 11% had maternal hyperglycaemia. Among smokers, each 23-nmol/l increase in serum 25-hydroxyvitamin D was associated with a reduction in the odds of maternal hyperglycaemia [odds ratio: 0.30 (95% CI: 0.13, 0.68)] after adjustment for parity, race/ethnicity, age, pre-pregnancy BMI, marital status, income, family history of diabetes, and gestational age of gestational diabetes mellitus screening. Among non-smokers, we found no association between early pregnancy vitamin D status and maternal hyperglycaemia. Conclusions Smoking status may modify the relationship between poor maternal vitamin D status and maternal hyperglycaemia.