Absence of expression of RhD by human trophoblast cells. 
Our purpose was to determine whether the RhD gene is expressed in trophoblast at any stage of gestation.  Trophoblast and fetal tissue were obtained from 18 pregnancies at 8 to 40 weeks' gestation.  Deoxyribonucleic acid and ribonucleic acid were extracted from trophoblast.  Complementary deoxyribonucleic acid was synthesized from ribonucleic acid, and reverse transcriptase-polymerase chain reaction was performed using primers specific for the RhD gene.  Deoxyribonucleic acid was extracted from fetal tissue to determine the fetal RhD status by means of polymerase chain reaction.  Antigen expression was also sought by analytic cytometric analysis (flow cytometry and immunocytochemistry) using a monoclonal anti-D antibody.  Trophoblast was studied from various combinations of RhD-positive and RhD-negative fetuses (on deoxyribonucleic acid) from mothers to find no RhD gene expression in any sample.  Flow cytometry and immunocytochemistry confirmed this by demonstrating no RhD antigen sites on trophoblast cells.  Contrary to a previous report, we conclude that the RhD gene is not expressed in human trophoblast in any trimester.