Detection and quantitation of fetomaternal hemorrhage

Failure to administer additional doses of Rh immune globulin (RhIG) to patients with excessive fetomaternal hemorrhage (FMH) is one of the causes of continued Rh isoimmunization. We compared the fetal cell ratio (FCR) with the other laboratory methods currently used at our hospital to quantitate FMH, ie, fetal cell preparation (FCP), RhIG cross-match with maternal serum, and indirect Coombs' testing 24 to 48 hours after administration of RhIG. The incidence of excessive FMH as detected by the various methods was 3.6% (cross-match), 9.6% (Coombs'), 18% (FCP), and 66% (FCR). The methods currently used do not accurately quantify FMH. The FCR is the most sensitive test but it has a high false-positive rate and thus does not appear to be clinically useful. We suggest that repeating the indirect Coombs' test may provide a practical alternative for determining the need for additional doses of RhIG.