Blood and urine collection: Fasting (>8 h) maternal blood samples were collected at entry to care and week 28 of gestation. Blood specimens were also collected at 1-hour of the 50g glucose challenge test. Fasting blood samples collected at each visit were immediately refrigerated and centrifuged at 4oC. Plasma and serum were preserved from each patient (at -70oC) until assayed. 20 ml of urine was collected at entry to care and week 28 in metal free plastic containers and stored at -70oC.