Thrombocytes are platelets. They have the important job of helping the blood clot to stop someone from bleeding. They circulate throughout the bloodstream, and when a blood vessel is damaged, within seconds they are at the damaged area. Platelets help decrease the blood flow in the area, change shape and seal the damage. In thrombocytopenia, there is a low number of platelets in the bloodstream.
Neonatal Alloimmune Thrombocytopenia
This is the most common cause of severe neonatal thrombocytopenia. It affects approximately one out of every 350 pregnancies, according to Daniel Ambruso, M.D., Professor in the Department of Pediatrics at the University of Colorado School of Medicine in "Current Diagnosis & Treatment: Pediatrics." All platelets have a group of proteins on their membrane called GP IIb/IIIa. There are two forms of this protein group. In neonatal alloimmune thrombocytopenia, the GP IIb/IIIa proteins on the platelets of the fetus are different from the GP IIb/IIIa proteins of the mother. The baby has inherited the other form of this protein group from the father. Platelets from the fetus cross the placenta and circulate throughout the bloodstream of the mother. Because the GP IIb/IIIa proteins on the platelets are different, the immune system of the mother sees them as foreign substances and her antibodies attack the platelets of the fetus. From 10 to 30 percent develop severe brain hemorrhaging by 20 weeks gestation.
Kasabach-Merritt Syndrome
Georgina Hall, M.D., explains this disorder in the December 2001 issue of the "British Journal of Haematology." Newborns with Kasabach-Merritt syndrome have a hemangioma, or a mass made out of many blood vessels, which can develop in various organs and even in the skin. Because the lining of the blood vessels within the hemangioma is developing too fast, platelets get trapped inside. There are now less platelets circulating throughout the bloodstream, so the bone marrow releases more platelets and more platelets become active. This results in clots being formed in the blood vessels throughout the body. The platelets and the clotting substances become used up, and the newborn now has severe thrombocytopenia and a disorder called disseminated intravascular coagulation, or DIC. There are clots throughout the body and at the same time, not enough platelets to stop any bleeding.
Neonatal Autoimmune Thrombocytopenia
A newborn may develop this thrombocytopenia if the mother has immune thrombocytic purpura or systemic lupus erythematosus. These are both autoimmune disorders, where the immune system attacks its own body instead of attacking foreign substances. Women with immune thrombocytic purpura, or ITP, have antibodies against any GP IIb/IIIa or Ib/9 protein group on the platelet membrane. In systemic lupus erythematosus, or SLE, women have antibodies against DNA. In "Current Diagnosis & Treatment: Pediatrics," Dr. Ambruso explains that the antibodies cross the placenta and enter the bloodstream of the fetus. This can lead to thrombocytopenia. Newborns who are being breastfed continue to receive the antibodies of the mother in the breast milk. Most newborns do not have any severe bleeding, but approximately 0.2 to 2 percent may have hemorrhages in the brain.
References
- British Journal of Haematology: Kasabach-Merritt Syndrome: Pathogenesis and Management
- "Current Diagnosis & Treatment: Pediatrics"; William Hay, Jr., M.D., Myron Levin, M.D., Judith Sondheimer, M.D., Robin Deterding, M.D.; 2009
