Xia J, et al. - Through a nested case-control study of 107 gestational diabetes (GDM) cases and 214 controls in the Fetal Growth Studies-Singleton Cohort, investigators prospectively and longitudinally analyzed the association of vitamin D status during early to mid-pregnancy with GDM risk. As early as the first trimester of pregnancy, maternal vitamin D deficiency (<50 nmol/L) was linked to an elevated risk of GDM. For women who remained deficient through the second trimester, the relationship was stronger. Vitamin D status assessment in early pregnancy may be clinically important and valuable for improving risk stratification and developing effective GDM primary prevention interventions. A 2.82-fold increased risk for GDM was seen with vitamin D deficiency at 10 to 14 gestational weeks; persistent vitamin D deficiency at 10 to 14 and 15 to 26 weeks of gestation had a 4.46-fold elevated risk for GDM vs with women persistently non-deficient.