FETAL RHD TYPING BY POLYMERASE CHAIN-REACTION IN PREGNANCIES COMPLICATED BY RHESUS ALLOIMMUNIZATION

Objective: To review the specificity and sensitivity of diagnostic tec hniques using the polymerase chain reaction (PCR) on amniotic fluid (A F) samples for the determination of fetal RhD status. Data Sources: A MEDLINE computerized search was conducted for January 1991 through Mar ch 1996 using the key terms ''polymerase chain reaction,'' ''rhesus,'' and ''RhD typing.'' Methods of Study Selection: All articles describi ng the use of PCR in AF for RhD typing were reviewed. Only cases in wh ich the results of PCR testing were confirmed by fetal or neonatal ser ology were included in the final analysis. Tabulation, Integration, an d Results: The results of PCR typing were compared with serology to de termine the sensitivity, specificity, and positive and negative predic tive values of DNA-based techniques. A total of 500 cases were reviewe d, in which four different sets of oligonucleotide primers were used. The sensitivity and specificity of PCR typing were 98.7% and 100%, res pectively, and the positive and negative predictive values were 100% a nd 96.9%, respectively. In five cases, an RhD-positive fetus was incor rectly diagnosed: Two fetuses died, one neonate needed exchange transf usions, and another neonate needed phototherapy in conjunction with a simple transfusion. The remaining infant was lost to follow-up. A theo retical model indicated that amniocentesis with PCR-based techniques f or fetal RhD typing would be associated with a fourfold reduction in p erinatal loss compared with funipuncture and serology for fetal typing . Conclusions: This lower rate of procedure-related loss makes RhD typ ing using AF the preferred method for assessing the fetal Rh status in cases of a heterozygous paternal genotype. (Copyright (C) 1996 by The American College of Obstetricians and Gynecologists.)