Non-invasive detection of fetal RHD status using maternal plasma is one of the few real advances in fetal medicine or obstetrics in recent years. DNA amplification of one or more region of the RHD gene can predict the fetal genotype with an accuracy of almost 99%.1 2 This means that invasive procedures (amniocentesis and chorionic villus sampling)—which carry a small but important risk of pregnancy loss and may also increase the risk of sensitisation in pregnancies at risk from fetal haemolytic disease—can be abandoned.

Non-invasive ascertainment of the fetal RHD genotype (and other red cell antigens) is now used routinely in the United Kingdom and elsewhere in the world.3 The technology, although labour intensive, is relatively simple and very reliable. In the accompanying study, Finning and colleagues assess the feasibility of applying a high throughput method for predicting RhD phenotype from fetal DNA in the plasma of pregnant women who are RhD negative.4

The incidence of RHD alloimmunisation has fallen greatly since the introduction of anti-RhD prophylaxis. In the 1960s prophylaxis was given …