Vitamin K deficiency bleeding of the newborn (VKDB) refers to spontaneous bleeding in a newborn caused by a deficiency of vitamin K dependent-coagulation factors. As vitamin K does not cross the placental barrier, is not present in breast milk, and is not synthesized in the sterile gut of a newborn, vitamin K levels are low in all neonates. VKDB is rare in industrialized countries because most children receive a vitamin K injection at birth. VKDB is categorized as early-onset (within 24 hours after birth), classic (within 4 weeks), or late-onset (between 2–8 months). Bleeding is usually intracranial, subgaleal, gastrointestinal, or nasal. Treatment is focused on managing the bleeding with, e.g., transfusions and restoring bleeding homeostasis by administering vitamin K.
- Without prophylaxis: affects 0.25–1.7% of newborns 
Epidemiological data refers to the US, unless otherwise specified.
The underlying cause is always a deficiency of vitamin K, which can be due to various factors:
- Exclusive breastfeeding: low vitamin K levels in breast milk (most important in late-onset VKDB)
- Low liver storage capacity
- Poor placental passage of vitamin K
- Vitamin K deficiency in the mother (e.g., because of therapy; most important in early-onset VKDB; maternal malnutrition)
- Underdeveloped intestinal flora (which produces vitamin K), e.g., due to premature birth
- Chronic diarrhea of the newborn
- Long-term antibiotic treatment in newborns
- Cholestatic diseases (e.g., biliary atresia)