Objectives: to determine the relationship between maternal hemoglobin (HbM) per gestational trimester and birthweight (BW). Methods: this was an analytical, cross-sectional observational study that included the prenatal records of494 pregnant women who delivered live newborns in the Department of Antioquia. The maternal health data collected included HbM and BW, and gynecological and obstetric, anthropometric, and maternal health-related data. The Mann-Whitney U test was applied, supplemented by effect size (ES) to compare