Embryology · Teratology and prenatal diagnosis
Warfarin embryopathy !
- Teratogen
Warfarin, a blood thinner, can disturb the embryo's bones and nose and, later, cause bleeding in the fetal brain.
Updated 2026-11-01
See it in 3D: Nasal bones · Nasal cartilages · Humerus · Femur
What it is
Warfarin is a vitamin K antagonist that crosses the placenta. Early in pregnancy it stops vitamin K–dependent bone and cartilage proteins from being activated, giving the classic embryopathy: nasal hypoplasia and stippled epiphyses. Later the risk is fetal bleeding with central nervous system damage. Heparin does not cross the placenta.
Key facts
- Mechanism: blocks gamma-carboxylation of vitamin K–dependent proteins.
- These include clotting factors and matrix proteins of bone and cartilage.
- Other findings: choanal atresia or stenosis, limb hypoplasia and short stature.
- Warfarin is also linked to miscarriage and stillbirth.
- It is a small molecule that crosses the placenta easily.
Critical period and mechanism
- Critical period: gestational weeks 6 to 9 for the skeletal defects.
- It inhibits vitamin K epoxide reductase, leaving proteins with gamma-carboxyglutamic acid residues inactive.
- Without those proteins, cartilage calcifies in abnormal spots (stippled epiphyses) and the nasal skeleton grows little.
- In the fetus, the lack of active clotting factors favours bleeding into the brain and other organs.
Prevention
- Preconception counselling for anticoagulated women to plan treatment.
- The treating team (cardiology and obstetrics) chooses the right anticoagulant for each stage of pregnancy.
- Medicines in pregnancy are decided with the treating professional, never stopped on one's own.
What it does to the embryo and fetus
- Hypoplastic nose with a depressed nasal bridge; breathing difficulty from choanal stenosis.
- Stippled calcifications of the epiphyses on X-ray; short limbs.
- From haemorrhage: microcephaly, hydrocephalus, Dandy-Walker, optic atrophy and intellectual disability.
- Miscarriage or stillbirth.
Test yourself
Think of the answer, then tap the question to see it.
What are the two classic findings of warfarin embryopathy?
Nasal hypoplasia and stippled epiphyses (chondrodysplasia punctata).
In which gestational weeks is the risk of warfarin embryopathy highest?
Between gestational weeks 6 and 9.
Why does heparin not cause this embryopathy?
It is a large, charged molecule that does not cross the placenta.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Congenital hydrocephalus: aqueductal stenosis
- Dandy–Walker malformation
- Skull: neurocranium, viscerocranium, sutures and fontanelles
- Limb development: the apical ectodermal ridge, ZPA and limb rotation
- Microcephaly
- Principles of teratology: critical periods, dose and genotype
Related conditions
In Pharmacology
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Teratogenic Medications (StatPearls Publishing (NCBI Bookshelf), 2024); Langman's Medical Embryology, 13th ed., ch. 9: Birth Defects and Prenatal Diagnosis (Wolters Kluwer, 2015).
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Representative model, for educational purposes only.