Fetal RhD typing by polymerase chain reaction in pregnancies complicated by rhesus alloimmunization.

OBJECTIVE

To review the specificity and sensitivity of diagnostic techniques using the polymerase chain reaction (PCR) on amniotic fluid (AF) samples for the determination of fetal RhD status.

DATA SOURCES

A MEDLINE computerized search was conducted for January 1991 through March 1996 using the key terms "polymerase chain reaction," "rhesus," and "RhD typing."

METHODS OF STUDY SELECTION

All articles describing the use of PCR in AF for RhD typing were reviewed. Only cases in which the results of PCR testing were confirmed by fetal or neonatal serology were included in the final analysis.

TABULATION, INTEGRATION, AND RESULTS: The results of PCR typing were compared with serology to determine the sensitivity, specificity, and positive and negative predictive values of DNA-based techniques. A total of 500 cases were reviewed, in which four different sets of oligonucleotide primers were used. The sensitivity and specificity of PCR typing were 98.7% and 100%, respectively, and the positive and negative predictive values were 100% and 96.9%, respectively. In five cases, an RhD-positive fetus was incorrectly diagnosed: Two fetuses died, one neonate needed exchange transfusions, and another neonate needed phototherapy in conjunction with a simple transfusion. The remaining infant was lost to follow-up. A theoretical model indicated that amniocentesis with PCR-based techniques for fetal RhD typing would be associated with a fourfold reduction in perinatal loss compared with funipuncture and serology for fetal typing.

CONCLUSIONS

This lower rate of procedure-related loss makes RhD typing using AF the preferred method for assessing the fetal Rh status in cases of a heterozygous paternal genotype.