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.