We report a case of materno-foetal transfusion in a phenotypically normal male foetus after death in utero at the 35th week of gestation. We have used cytogenetic and polymerase chain reaction (PCR) microsatellite analysis to determine the presence of maternal cells in foetal blood collected by intracardiac puncture. In the intracardiac blood sample, maternal cells were estimated to comprise between 5 and 10% of nucleated foetal blood cells. When there is a suspicion of foetal genetic pathology, it is necessary to be aware that the foetal blood karyotype may be misrepresentative, as the analysed blood cells can indeed be of maternal origin.