Iron status assessment
Serum ferritin was measured by electrochemiluminescence immunoassay kits (Roche Diagnostics GmbH, Cobas e601 analyzer, Germany), and hemoglobin was measured by colorimetry. The levels of SF (reference range, 13.00 - 150.00 μg/L) and Hb (reference range, 110 - 150 g/L) were evaluated respectively. Based on the recommendation for diagnosis of ID in pregnancy18, women who had serum ferritin levels < 20μg/L were classified as group ID.