<h4>Background</h4>As anaemia during pregnancy is common in China, we sought to investigate the incidence and influencing factors on maternal anemia in the northern part of China.<h4>Methods</h4>We conducted a prospective cohort study from October 2020 to June 2024 at 13 hospitals in China, enrolling 18 416 pregnant women aged ≥18 years who had regular prenatal examinations, Their data (location, history of anaemia, and haemoglobin (Hb) test results) were collected via an app data collection platform. This evidence concerns the gene GSTM1 and anemia (phenotype).