Cause:Maternal antibody, usually vs RhD, but now, w liberal Rhogam use, Kell antibodies account for 10% of all cases (Nejm 1998;338:798); transplacental passage of 7S (IgG) antibody
Pathophys:Fetal cells cross placenta, mostly at birth, and sensitize mother’s immune system; antibody later, during subsequent pregnancies, crosses to hemolyze fetal rbc’s although can occur even in 1st pregnancy. Antibody-coated rbc’s result in hemolysis and elevated bilirubin production, which postpartum, with acidosis and hypotension, can cause kernicterus, since unconjugated bilirubin can cross the blood–brain barrier and is toxic to the brain (Clin Perinatol 1988;15:4). Pre- and postpartum severe anemia causes CHF, called hydrops fetalis prepartum
Kell antibodies cause not only hemolysis but also blocked erythropoietin effects on rbc precursors (Nejm 1998;338:798)
ABO incompatibility protects against Rh sensitization developing by eliminating incompatible cells quickly before sensitization can occur, ie, a sort of built-in Rhogam injection?
Very rare now with Rhogam rx, better ob outcomes w fewer lower birth order children (Am J Publ Hlth 1998;88:209)
Sx:Spontaneous abortion at 26+ weeks in woman with previous sensitizing pregnancy
Si:Postpartum anemia, jaundice, CHF, and hydrops fetalis
Intrauterine hydrops fetalis; with kernicterus, spasticity, deafness, and other CNS damage
r/o other neonatal jaundice causes (see Neonatal Jaundice)
Lab:
Chem:Bilirubin elevated; an indirect >20 mg % can cause kernicterus (staining of brain); follow q 4 h postpartum
Blood sugar; keep normal; hypoglycemia can worsen hepatic conjugation of bilirubin too
Amniotic fluid bilirubin elevated, used to determine need for intrauterine exchanges
Hem:Coombs test positive, direct and indirect; retics low for 3-5 wk, no matter how anemic baby is
Serol:Mother’s titer >1/64 and increases from 1st to 3rd trimester; RhD PCR analysis of fetal DNA in maternal blood is reliable from 2nd trimester on (Nejm 1998;339:1734)
Xray:Ultrasound detects anemia (Nejm 2000;342:9) and later fetal edema (Nejm 1986;315:430)
Rx:
Prevent w Rhogam, about 1 cc within 72 h of delivery if Rh-positive child or if abortion; adjust dose by Kleihauer-Betke test of fetal rbc’s in maternal circulation; 95% effective; give also at 28-wk gestation to get final 5%
Stop breastfeeding
Exchange transfusions, intrauterine (Nejm 1986;314:1431), or postpartum if cord bilirubin >6 mg % or serum headed above 20 at >0.5 mg %/h