A moderate decrease in factors II, VII, IX, and X normally occurs in all newborn infants by 48–72 hr after birth, with a gradual return to birth levels by 7–10 days of age. This transient deficiency of vitamin K–dependent factors is probably due to lack of free vitamin K from the mother and absence of the bacterial intestinal flora normally responsible for the synthesis of vitamin K. Rarely, in term infants and more frequently in premature infants, accentuation and prolongation of this deficiency between the 2nd and 7th days of life result in spontaneous and prolonged bleeding. Breast milk is a poor source of vitamin K, and hemorrhagic complications are more frequent in breast-fed than in formula-fed infants. This classic form of hemorrhagic disease of the newborn, which is responsive to and prevented by vitamin K therapy, must be distinguished from disseminated intravascular coagulopathy and from the more infrequent congenital deficiencies of one or more of the other factors that are unresponsive to vitamin K.
http://easypediatrics.com/hemorrhagic-disease-of-newborn
