Anti-C(w) alloimmunization presenting as hydrops fetalis

C(w) is a low frequency red cell antigen that belongs to the Rh blood groups system. While not uncommon, anti-C(w) is rarely associated with clinically significant haemolytic disease of the newborn (HDN). When it does occur, it is often subclinical or of mild to moderate clinical severity. In the majority of pregnancies it is considered to be a naturally occurring antibody and has not been reported to cause hydrops fetalis or stillbirth. We report a case of anti-C(w) alloimmunization, which was associated with significant anaemia and hydrops fetalis, presenting at 35 wk gestation.

Pregnancies affected by anti-C(w) merit closer scrutiny. Consideration should be given to performing more frequent antenatal ultrasound assessments to detect hydrops fetalis. This may help to support the need for more invasive procedures (cordocentesis and intrauterine transfusions).