Detecting Free Fetal DNA In Maternal Plasma To Prenatally Diagnose Fetal Blood Groups

Objective:Aiming at the structural characteristics of ABO and RhD genes,a method for accurately and quickly predicting fetal blood groups using fetal free DNA in pregnant women’s plasma was established,and a new idea for non-invasive prenatal diagnosis of hemolytic disease of the fetus and newborn was found.Methods:(1)The healthy pregnant women with blood type O who came to our hospital for antibody screening were selected as the research subjects.The first pregnancy was single and the husband was non-O blood type.A total of 83 pregnant women’s plasma samples were collected to extract fetal free DNA.Non-O and B primers were designed for the conservative characteristic mutations of the ABO gene,and the fetal ABO genotype was detected by real-time PCR.For samples without amplification of both,the presence of fetal free DNA was verified by detecting the RASSF1 A gene.Fetal umbilical cord blood was collected from pregnant women after delivery,and the neonatal ABO phenotype was determined by serological methods,and compared with the results of prenatal genetic prediction.(2)RhD-negative pregnant healthy women who were pregnant and single-born came to our hospital for prenatal examination were selected as research subjects,and RhD-positive husbands were collected.A total of 25 pregnant women’s plasma samples were collected to extract fetal free DNA.The selected regions of the RhD gene(intron 4,exon 5,7,and 10)were amplified by real-time PCR to detect the fetal RhD blood group,and the fetal blood group was RhD negative to detect the RASSF1 A gene to verify the fetal free DNA.presence.Fetal umbilical cord blood wascollected after delivery,the RhD phenotype of the newborn was determined by serological methods and compared with the results of prenatal genetic prediction.Results:The 83 plasma samples of pregnant women with blood type O,79 prenatal fetal ABO gene test results were consistent with the serological blood group of postpartum neonates: the accuracy of type A was 91.30%(21/23 cases),and the accuracy of type B The rate was 97.22%(35/36 cases),the accuracy of type O was 100.00%(23/23 cases),and fetal free DNA was not extracted in one case.Among 25 RhD-negative pregnant women’s plasma samples,23 samples had the same prenatal genetic testing with postpartum serological method to detect RhD blood group.One sample was classified in the uncertainty group,and the overall accuracy of the method was 92%(23/25)This method has a sensitivity of 100%,a specificity of 85.7%,a positive predictive value of94.4%,and a negative predictive value of 100%.Conclusion:The fetal free DNA present in the peripheral blood of pregnant women can be used for non-invasive prenatal diagnosis of fetal blood types,and a new technical method has been found for the early diagnosis of hemolytic disease of the fetus and newborn.