Transplacental haemorrhage (TPH) may occur following a sensitisng event during pregnancy or at delivery and can lead to RhD immunisation. Assessment of TPH is an important element in determining the amount of anti-D to be administered to a RhD-negative mother following a sensitising event or after delivery of an RhD-positive infant.

The joint Consensus Conference of the Royal College of Physicians of Edinburgh/Royal College of Obstetricians and Gynaecologists on anti-D prophylaxis stated that 1–2% of RhD-negative pregnant women at risk still become sensitised.