Fetal warfarin syndrome is a disorder of the embryo which occurs in a child whose mother took the medication warfarin (brand name: Coumadin) during pregnancy. Resulting abnormalities include low birth weight, slower growth, intellectual disability, deafness, small head size, and malformed bones, cartilage, and joints. Warfarin is an oral anticoagulant drug (blood thinner) used to reduce blood clots, deep vein thrombosis, and embolism in people with prosthetic heart valves, atrial fibrillation, or those who have had ischemic stroke. Warfarin blocks the action of vitamin K, causing an inhibition of blood clotting factors and the pro-bone-building hormone osteocalcin. Warfarin is a teratogen which can cross from the mother to the developing fetus. The inhibition of clotting factors can lead to internal bleeding of the fetus while the inhibition of osteocalcin causes lower bone growth. As well as birth defects, warfarin can induce spontaneous abortion or stillbirth. Because of this, warfarin is contraindicated during pregnancy. Signs and symptoms The key symptoms, visible at birth, vary between individuals exposed to warfarin in utero. The severity and occurrence of symptoms is dose dependent with higher doses (>5 mg warfarin daily) more likely to cause immediately noticeable defects. The period of pregnancy in which warfarin is administered can affect the category of defects which develop. Warfarin taken in the first trimester of pregnancy is more likely to result in physical abnormalities while warfarin taken in the second and third trimester more commonly causes abnormalities of the central nervous system. The more extreme symptoms such as severe intellectual disability, blindness and deafness occur more often when warfarin is used throughout all three trimesters. Growth Babies born with fetal warfarin syndrome may have a below-average birth weight and do continue to grow at a reduced rate. Facial features Children with fetal warfarin syndrome show many otolaryngological abnormalities consistent with abnormal bone and cartilage growth. Children may present with hypoplasia of the nasal ridge and a deep groove at the midline of the nose, thinned or absent nasal septum, choanal atresia; a narrowing the airway at the posterior nasal cavity, cleft lip and laryngomalacia; large soft protrusions into the larynx. These facial defects and narrowing of the airways often lead to respiratory distress, noisy breathing and later; speech defects. Narrow airways often widen with age and allow for easier breathing. Dental problems are also seen with abnormally large dental buds and late eruption of deciduous teeth. Development of