Fetal RHD genotyping after bone marrow transplantation

BACKGROUND Fetal RHD genotyping allows targeted diagnostic testing, fetal surveillance, and eventually intrauterine treatment to D‐alloimmunized pregnant women who carry an RHD+ fetus. However, false‐positive and false‐negative results of noninvasive prenatal fetal RHD genotyping have been described due to a variety of causes. In this case report we present two cases where noninvasive fetal RHD typing was complicated by a previous bone marrow transplantation (BMT). CASE REPORT We describe two women with a history of allogeneic BMT in early childhood. Both were born D+ and received a transplant of their D– male sibling. Anti‐D were detected during pregnancy in one of them. The biologic father of this pregnancy was D+. In both cases polymerase chain reaction procedures specific for RHD on maternal plasma DNA were positive whereas a D– neonate was born in one case (Case 1). CONCLUSION False‐positive results of noninvasive fetal RHD genotyping occur in D+ women transplanted with marrow of a D– donor, due to circulating cell‐free DNA originating from nonhematopoietic tissue. The cases highlight that health care professionals and laboratories should be aware that allogeneic BMT can be a cause for false‐positive results in fetal RHD genotyping with cell‐free DNA in maternal plasma, and likewise the wrong fetal sex can be reported in the case of a male donor and a female fetus. Based on one of the cases we also recommend giving D– blood products to young female patients who receive a BMT of D– donors.