Rh isoimmunization: a 24 year experience at Duke University Medical Center.

A retrospective analysis was made of Rh-sensitized patients delivered of their babies at Duke University Medical Center during a 24 year period. Records of 202 obstetric patients representing 280 sensitized pregnancies from a pool of 39,910 deliveries were analyzed for past obstetric history, blood group information, antibody determinations, amniocentesis data, and details of the pregnancy and delivery. The medical records of the corresponding infants were analyzed for their neonatal course. A severity index (SI) was devised to classify the degree of severity of the erythroblastosis fetalis. A significant correlation between SI and the delta OD450 of amniotic fluid, umbilical cord hematocrit, and bilirubin was noted. The evaluation of amniotic fluid delta OD450 is considered to be the cornerstone of clinical management. Twenty-nine patients had initial Liley zone 1 determinations which decreased to delta OD450 = 0.000; however, only 10 of 29 (34.5%) of the infants were unaffected, and 13 of 29 (44.8%) had mild sensitization, four of 29 (13.8%) had moderate sensitization, and two of 29 (6.9%) had severe sensitization. The previously held concept of "critical titer" as a guide for initiating amniocentesis is challenged, and the recommendation is made that amniocentesis for amniotic fluid determination should be undertaken in any patient with a positive indirect Coombs titer.