Inherited thrombophilia in pregnancy: who needs a plan?

What does the evidence say about inherited thrombophilia in pregnancy?

1. Factor V Leiden affects a clotting protein and increases the likelihood of abnormal clots, but many carriers never have one. The number of affected gene copies and other risk factors influence the assessment. A relative's experience is not an individual forecast. 1
2. Prothrombin thrombophilia usually involves a particular F2 variant. Pregnancy, surgery, immobility-related circumstances, family history, and additional clotting conditions can contribute to risk. Bring the exact genetic result rather than relying on the broad label thick blood. 2
3. ASH pregnancy guidance distinguishes a first-clot risk assessment from care after a previous venous clot. It does not recommend routine pregnancy anticoagulation for every inherited thrombophilia. Decisions vary by condition, family and personal history, and whether the question concerns pregnancy or postpartum. 3
4. Research linking Factor V Leiden to some placental and pregnancy complications is not uniformly established. The presence of a variant should not be assumed to explain a particular miscarriage or every pregnancy symptom. Ask what evidence supports the proposed investigation or medicine in your case. 1
5. A painful swollen limb, chest pain, sudden breathing difficulty, or fainting can signal an urgent problem. Seek prompt assessment even if the clotting risk was previously described as low. A risk assessment guides planning; it does not exclude a new clot. 4

When should inherited thrombophilia planning be reviewed?

• First trimester. Early in pregnancy, verify the specific result and personal and family clotting history.
• Second trimester. During follow-up, report new risk factors such as admission, procedures, or major changes in mobility.
• Third trimester. Before birth, confirm the delivery and postpartum plan and how to communicate any anticoagulant doses.

Questions to discuss with your care team