Prothrombin (Factor II) Levels During Pregnancy
Prothrombin (factor II) increases during pregnancy as part of the physiologic hypercoagulable state that develops to prevent excessive bleeding during delivery. 1
Changes in Coagulation Factors During Pregnancy
Pregnancy induces significant alterations in the hemostatic system, creating a hypercoagulable state that serves as a protective mechanism against hemorrhage during delivery. These changes include:
Increased Coagulation Factors:
- Factor II (prothrombin) increases during pregnancy 1
- Fibrinogen increases markedly, reaching highest levels in the first weeks of pregnancy 1
- Factors VII, VIII, IX, X, and XII also increase 1
- Von Willebrand factor increases 1
Decreased Anticoagulant Factors:
- Protein S levels fall 1
- Protein C levels decrease 1
- Resistance to activated protein C increases in second and third trimesters 1
Changes in Fibrinolytic System:
- Decreased fibrinolysis 1
- Increased plasminogen activator inhibitor-1 (PAI-1) and PAI-2 1
- Reduced levels of available circulating plasminogen activator 1
Clinical Implications
The hypercoagulable state of pregnancy, including elevated factor II, contributes to a 4-10 fold increased risk of thrombotic events during pregnancy and postpartum 2. This is particularly important in women with underlying thrombophilias.
Thrombotic Risk Assessment:
- The risk of venous thromboembolism is increased 4-6 fold during pregnancy, with greatest risk in the postpartum phase 1
- Women with factor V Leiden mutation, prothrombin G20210A mutation, or both have significantly higher thrombosis risk during pregnancy 3, 4
- Arterial strokes are more common during pregnancy, while venous occlusion is more common during the puerperium 1
Laboratory Interpretation During Pregnancy:
- When interpreting coagulation tests during pregnancy, it's important to use pregnancy-specific reference ranges
- PT ratio and APTT ratio should be used with a ratio ≥1.5 as cut-off for coagulopathy, rather than absolute values in seconds 1
- D-dimer levels increase progressively throughout pregnancy, peaking in the third trimester 1
Monitoring Considerations
The hypercoagulable state of pregnancy requires careful monitoring, especially in women with additional risk factors for thrombosis:
- Factor VIII increases gradually during pregnancy, which might mask lupus anticoagulant by shortening the APTT 1
- Antiphospholipid antibody positivity may fluctuate during pregnancy 1
- Laboratory test results obtained during pregnancy should be repeated postdelivery to confirm findings 1
Postpartum Changes
The hemostatic changes noted during pregnancy typically normalize within 4-6 weeks after delivery, though some parameters may take longer to return to baseline 5.
The hypercoagulable state of pregnancy, characterized by increased prothrombin (factor II) and other procoagulant factors, serves as a physiologic adaptation to reduce bleeding risk at delivery, but also increases thrombotic risk that requires appropriate management in high-risk women.