C-Reactive protein has been associated with several complications of pregnancy. The aims of the present study were: (1) to evaluate a turbidimetric immunoassay for the measurement of C-reactive protein; and (2) to investigate the chronological changes of the levels of this protein from preconception throughout normal pregnancy and its relationship with variables associated with preconception and pregnancy outcome. Inter-assay imprecision was <5% for C-reactive protein >1 mg/L and 18% at a mean value of 0.33 mg/L. The limit of detection was 0.10 mg/L. The method was linear between 0.10 and 30 mg/L. There were no observed interferences from jaundice, hemolysis, lipemia or paraproteinemia at the levels studied. There was good agreement with the nephelometric method. A total of 39 women were studied at preconception, at 8, 20 and 32 weeks of pregnancy, and in labor. Preconception C-reactive protein concentration was 1.17+/-0.18 mg/L and increased (p<0.001) throughout pregnancy up to 5.69+/-0.82 mg/L. Body mass index at preconception and weight gain during pregnancy were the main factors associated with this increase in C-reactive protein.