It has been suggested that the ABO blood group of a patient and her pa
rtner influence the clinical outcome for patients having a pregnancy w
ith a complete hydatidiform mole (CHM). Since CHM lack red blood cells
, it has not previously been possible to type CHM serologically and in
vestigate the relationship between the blood group of the CHM and that
of the patient. In the present study we have demonstrated the feasibi
lity of using molecular genotyping to determine the ABO genotype of CH
M, the ABO genotype being consistent with the androgenetic origin of C
HM in all cases. In the series of 48 cases of CHM, the requirement for
chemotherapy was not significantly different in those patients with a
CHM of like blood group compared with those with a CHM of unlike bloo
d group.