Massive foeto-maternal transfusion: how long are foetal blood cells detectable in the maternal circulation?

Massive foeto-maternal transfusion (FMT) is the passage into the maternal circulation of >20% of foetal blood volume. It is associated with high perinatal morbidity and mortality1. FMT affects approximately 0.3-1:1,000 births and in non-complicated near-term pregnancies is frequently idiopathic1.Clinical manifestations are non-specific and are mostly represented by a decrease in active foetal movements (AFM). Foetal anaemia can be suggested by a sinusoidal rhythm on cardiotocography (CTG) and by high peak systolic velocity (PSV) of the middle cerebral artery (MCA); both tests, however, are liable to yield false negative results1. The conclusive diagnosis of FMT is based on maternal laboratory blood tests such as the Kleihauer-Betke, although the gold standard is currently flow cytometry which has been proven to be more sensitive and time-saving2. However, the latter test is not always available, and therefore FMT is to be considered when other possible origins of neonatal anaemia have been excluded. We aim to demonstrate the long-lasting persistence of foetal blood cells in the maternal circulation in a case of massive FMT. These data are useful in a clinical scenario when FMT is not immediately suspected or investigated.