Which thrombophilia laboratory tests are affected during pregnancy?

From the Guidelines

In pregnancy, the following thrombophilia laboratory tests are affected:

• Protein S levels, which typically decrease 1
• Antithrombin levels, which may decrease slightly 1
• Lupus anticoagulant and anticardiolipin antibody levels, which may remain unchanged or fluctuate 1
• Factor VIII and von Willebrand factor levels, which usually increase 1
• Homocysteine levels, which may be affected by folate supplementation 1
• Activated protein C resistance, which may be affected by pregnancy-induced changes in coagulation factors 1
• FIBTEM A5 and A15, which have been used to detect fibrinogen levels < 1.5 g/L in postpartum hemorrhage 1
• ROTEM parameters, such as clotting time, clot formation time, and maximum clot firmness, which can be affected by pregnancy and postpartum hemorrhage 1

It is essential to interpret these lab results in the context of pregnancy and consider the clinical presentation and medical history of the patient. The use of viscoelastic testing, such as TEG or ROTEM, can provide valuable information on the coagulation status of pregnant women, especially those at risk for thrombosis or postpartum hemorrhage 1.

Some key points to consider when interpreting these lab results include:

• The normal range for clotting times may be different in pregnant women compared to non-pregnant women 1
• The levels of certain coagulation factors, such as factor VIII and von Willebrand factor, may increase during pregnancy 1
• The presence of lupus anticoagulant or anticardiolipin antibodies may require special consideration when interpreting lab results 1
• The use of antithrombotic therapy, such as low-dose aspirin or enoxaparin, may affect lab results 1

From the Research

Thrombophilia Laboratory Tests Affected During Pregnancy

The following thrombophilia laboratory tests are affected during pregnancy:

• Protein C (PC): results show large variability 2, and levels may increase throughout the first 22 weeks of pregnancy 3
• Antithrombin (AT): decreases slightly 2, and levels may be decreased in patients with preeclampsia 4
• Protein S free (PS free) and protein S activity (PS activity): decrease significantly 2, with a mean level of 46% for protein S activity 3
• Activated protein C resistance (APCR): the APCR ratio is constant, but the levels of protein S are decreased in patients with diagnosed thrombophilia 4
• Homocysteine: levels may be elevated in patients with hyperhomocysteinemia 4

Physiological Changes During Pregnancy

Pregnancy is associated with procoagulant physiological changes, which can make interpretation of coagulation parameters difficult 2, 5. The normal physiology of pregnancy may be prothrombotic, with evidence for increased markers of activated coagulation and coagulation factors 5.

Clinical Implications

Testing for thrombophilia should be carried out in women with adverse pregnancy outcomes in their history, who are planning pregnancy, to start anticoagulant prophylaxis 4. The diagnosis of protein C and protein S deficiency during pregnancy is limited by the use of non-pregnant reference ranges, and altered reference ranges for these proteins during early pregnancy should be considered 3.