A group of hereditary disorders characterized by prolonged bleeding and sometimes excessive bleeding. There may be bleeding into joints, gastrointestinal tract, and urinary tract. On laboratory the activated partial thromboplastin (PTT) time is prolonged. However, the prothrombin time (PT) and bleeding time are normal.

Hemophilia A and hemophilia B (Christmas disease) account for most cases of hemophilia. Hemophilia A is caused by a lack of the blood clotting protein factor VIII, and hemophilia B is caused by a lack of the blood clotting protein factor IX. Hemophilia A is 7 times more common than hemophilia B. Both diseases are caused by a defective gene located on the X chromosome.

Since the male contributes the X chromosome to form female and the Y chromosome to form male offspring, all the daughters of a male affected with hemophilia will be carriers of the defective gene. The daughters of a hemophiliac male will pass the gene to 50% of their male offspring who in turn will have hemophilia.

For the newborn at risk for hemophilia it is best to avoid fetal scalp electrodes, forceps, and vacuum extraction. The pediatrician should be notified of the baby's possible hemophilia. Circumcision, if desired, should be delayed as well as intramuscular injections until coagulation studies are completed and the diagnosis of hemophilia is either established or ruled out.