oa Molecular Diagnosis and Vaccines - Free fetal DNA in maternal blood: new horizons in non-invasive prenatal diagnosis; prediction of fetal RhD status in RhD negative mothers



RhD incompatibility between the pregnant mother and her fetus is a significant problem due to the possibility of haemolytic disease of the fetus and newborn (HDF/N). In paternal RhD heterozygosity antenatal diagnosis of fetal RhD status for all RhD negative pregnant women is highly desirable for both financial and ethical reasons. Free fetal DNA in maternal plasma has been proved to be a good source of genetic prenatal non invasive diagnosis. Different sensitivities have been quoted on its use to detect RhD status in RhD negative pregnant women. In this study we aimed to assess whether fetal DNA in maternal plasma can be used to determine the fetal RhD status. The reliability of the PCR technique at different gestational ages was evaluated. Plasma and serum samples were collected from 40 RhD negative women at different stages of pregnancy. Samples were genotyped for RhD using polymerase chain reaction. Cord blood RhD serologic examination was done for all delivered babies as a gold standard. Samples from ten non-pregnant women (5 RhD+ and 5 RhD-) were included as controls for genotyping. Twenty seven babies were serologically proven to be RhD positive and thirteen were RhD negative. Starting from the second trimester, the PCR based assay accurately (100%) predicted the fetal RhD status and showed 100%specificity and sensitivity. No false positive results were reported.There was one false negative case in the first trimester. Maternal plasma samples were better than maternal serum (sensitivity96% vs 88%). It is concluded that maternal free fetal DNA is a promising non-invasive prenatal diagnosis. It can accurately be used starting from the second trimester to predict RhD positive cases where further measures to protect the fetus would be used.


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