Noninvasive Antenatal Diagnosis of Fetal RhD Status

Introduction: Fetal cell-free nucleic acids within the blood stream of a pregnant woman come from fetal genetic material which can be acquired by simple venipuncture that reduces any risk to a minimum. Fetal cell-free DNA can be detected in the mother's blood stream in the 5th gestation week at the earliest. That enables fetal genotyping at the earliest possible stage of pregnancy which is best done in the 12th gestation week.

Aim: To determine fetal RhD status at RhD negative pregnant women where the father is a heterozygote, Dd.

Materials and Methods: The research includes 1540 RhD negative pregnant women, out of which at 30 of them the RhD fetal status had been detected by a PCR technique from the mother’s plasma. The RhD fetal status was confirmed after delivery by serologic analysis at 27 newborn babies.

All research patients were submitted to serologic immunohematology testing: blood group typing of red blood cell antigens, screening of irregular anti-red blood cell antibodies. Fetal RhD status was determined by the plasma of RhD negative pregnant women using the real-time PCR technology in the period from the 12th gestation week until the 31 gestation week. The biological fathers of all 30 fetuses were phenotyped as heterozygote to the RhD antigen. The results showed that 30% of the fetuses are RhD negative, and 70% are RhD positive.

Conclusion: The noninvasive fetal RhD genotyping is not only one precious tool in the management of RhD alloimmunised pregnancies, but it also allows antenatal anti-D immunoglobulin prophylaxis exclusiveness for only non-immunized RhD pregnant women carrying RhD positive fetus. Taking into consideration that 30% of the RhD negative pregnant women that carry a RhD negative fetus receive antenatal RhIG prophylaxis with no absolute need for it.

At RhD alloimmunised pregnant women the noninvasive genotyping of the fetal blood group enables an easy and safe method in determination of a fetal risk from a hemolytic disease, and at the same time evading a vast laboratory and clinical monitoring of RhD antigen-negative fetal cases.