Warfarin in Pregnancy — Is It Safe?
Last reviewed: · Source: US FDA drug label database
Warfarin is contraindicated in pregnancy — it causes fetal warfarin syndrome and bleeding. Heparin is the safe anticoagulant in pregnancy.
Is it safe to take Warfarin with Pregnancy?
Warfarin should not be used in pregnancy, particularly in the first trimester (weeks 6-12) and third trimester. It crosses the placenta and causes fetal warfarin syndrome (nasal hypoplasia, bone changes, eye abnormalities) and fetal haemorrhage. Women who require anticoagulation in pregnancy (e.g. those with mechanical heart valves, antiphospholipid syndrome, or DVT history) must switch to heparin or low-molecular-weight heparin (LMWH) such as enoxaparin, which does not cross the placenta.
How do Warfarin and Pregnancy interact?
Warfarin inhibits vitamin K-dependent clotting factors (II, VII, IX, X). It readily crosses the placenta and inhibits the fetal coagulation system. The embryo and fetus lack the ability to compensate, leading to bleeding and impaired bone/cartilage development (vitamin K-dependent proteins are also involved in bone formation). First-trimester exposure is most teratogenic; third-trimester exposure risks fetal intracranial haemorrhage during delivery.
Data sourced from the US Food and Drug Administration (FDA) drug label database: FDA warfarin drug label — pregnancy contraindication; OpenFDA drug label data.
Who should be careful?
All women of childbearing age taking warfarin should discuss pregnancy planning with their anticoagulation team. If pregnancy occurs on warfarin, seek urgent medical review.
What if I've already taken Warfarin and Pregnancy?
If you are taking warfarin and discover you are pregnant, seek urgent medical review — ideally with a haematologist and obstetrician. Do not stop suddenly without guidance, and transition to LMWH heparin will be arranged.
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Frequently Asked Questions
Can I take warfarin during pregnancy?
No. Warfarin crosses the placenta and causes fetal warfarin syndrome and bleeding. Women needing anticoagulation in pregnancy are switched to heparin or LMWH.
What anticoagulant is safe in pregnancy?
Low-molecular-weight heparin (LMWH, e.g. enoxaparin/Clexane) does not cross the placenta and is the standard anticoagulant used during pregnancy.
I am on warfarin and pregnant — what should I do?
Contact your GP or anticoagulation clinic urgently. You will be transitioned to LMWH heparin. The sooner this happens, the better.
What is fetal warfarin syndrome?
Fetal warfarin syndrome occurs from first-trimester warfarin exposure and causes nasal bridge hypoplasia (flattened nose bridge), stippled bone calcifications, eye abnormalities, and developmental delays.