Haemolytic disease of the fetus and newborn due to anti-Fy(a) and the potential clinical value of Duffy genotyping in pregnancies at risk.

Haemolytic disease of the newborn (HDN) caused by anti-Fy(a) is uncommon and usually mild. Current guidelines recommend that pregnant women with anti-Fy(a) are monitored less rigorously than those with anti-D, -c or -K. However, in a review of our recent experience of 68 pregnancies where anti-Fy(a) was detected, three were identified where the fetus was severely anaemic; in two cases the fetus received intrauterine transfusions. Our data suggest that pregnancies in which anti-Fy(a) is detected at significant titres (> 64) should be closely monitored in a similar way to pregnancies where other 'significant' antibodies are present. Moreover, in the presence of high or rising antibody titres, if the father is heterozygous and functional assays suggest the antibody is active, then fetal genotyping should be offered to help plan the future management of that pregnancy.