PRENATAL-DIAGNOSIS OF THE FETAL RHC GENOTYPE FROM PERIPHERAL MATERNALBLOOD

Objective: To determine the fetal Rhc genotype by using the polymerase chain reaction (PCR) amplification procedure and maternal blood at th e different steps of the fetal cell enrichment process. Methods: Mater nal peripheral venous blood samples were obtained from 11 pregnant wom en homozygous for the C antigen before amniocentesis. Three were not a lloimmunized and eight were alloimmunized. The fathers were known to b e heterozygous or homozygous for the c antigen by serologic testing. T he mononuclear cell layer was isolated from maternal blood and now sor ted using monoclonal antibodies to CD36 or CD71 and glycophorin A. Thi s was followed by PCR of the blood, mononuclear cells, and the sorted cells with allele-specific primers to RhCc genes. Gel electrophoresis was performed to predict fetal Rhc genotype. The fetal RhCc genotype w as confirmed by serologic and DNA testing. Results: All infants were p ositive for the Rhc gene. The positive fetal Rhc genotype was determin ed correctly in three of the 11 maternal blood samples without enrichm ent, in six of the nine mononuclear cell samples, and in seven of the eight sorted cell samples. The fetal genotype from one sorted sample w as predicted to be homozygous C. One infant was determined by serology on cord blood to be negative for the c antigen, but repeated infant D NA amplification was consistent with the c genotype. Conclusion: Nonin vasive fetal Rhc genotyping can be determined by PCR amplification of the rare fetal cells in maternal blood. These data reaffirm, that enri chment of maternal blood for fetal cells is necessary to improve the s ensitivity of the test. (C) 1998 by The American College of Obstetrici ans and Gynecologists.