Plasma antithrombin III activity in normal pregnancy

The incidence of thromboembolic phenomena increases in pregnancy. Antithrombin III has been implicated as a possible etiologic factor for the increase of thromboembolic phenomena in women receiving exogenous estrogens. In a study of normal obstetric, postpartum, and oral contraceptive patients, no significant change in antithrombin III activity could be detected in a plasma-based assay within and among these groups. It is hypothesized that a decrease in antithrombin III activity is not a cause of increased thromboembolic phenomena during normal pregnancy and oral contraceptive use.