Abstract
The author introduces the reader to a new method of non-invasive prenatal diagnosis, non-invasive RhD genotyping of the fetus, summarizes its advantages and disadvantages and discusses why it is not part of routine examinations in the USA. The author summarizes that non-invasive RhD genotyping of the fetus can be used usually in anti-D alloimmunized pregnancies at risk of fetal erythroblastosis (hemolytic disease of the fetus), if the biological father of RhD is positive heterozygous.
If the fetus is RhD negative, it is not at risk of maternal alloimmunization. It also draws attention to the possibility of using this test in non-alloimmunized mothers who receive anti-D prophylaxis in the 28th week of pregnancy.
The gynecologist then has the option of administering prophylaxis only to a mother with a RhD-positive fetus. The author describes in detail the methodological procedure, from the collection of maternal blood, through DNA amplification and evaluation of the PCR amplification result, but unfortunately on gel electrophoresis (and not in a real-time PCR system).
This procedure is not recommended for fetal RhD genotyping, and was used only in the early stages - shortly after the discovery of fetal DNA in the maternal circulation. Classical PCR with gel electrophoresis evaluation is less sensitive than commonly used real-time PCR, which is now considered the only suitable methodological approach to the successful detection of fetal nucleic acids that occur in the maternal circulation in low concentrations during pregnancy, from about 20 copies. / ml maternal plasma.
Surprisingly, this methodological procedure is mentioned in the article, as most of the works cited by the author use real-time PCR for fetal genotyping for RhD. The author also states that non-invasive RhD fetal genotyping can generate false positive and false negative results.
Non-invasive RhD genotyping of fetal peripheral blood is now performed routinely in some European countries (Great Britain, France, the Netherlands). The EU-supported SAFE project (Special Non-Invasive Advances in Fetal and Neonatal Evaluation, Network of Excellence, LSHBCT-2004-503243), in which a total of 50 partners (47 European and three outside the EU) participate, aims at Europe-wide standardization of this technology. for use in clinical routine practice.
In the Czech Republic, we now perform non-invasive RhD genotyping of the fetus routinely, especially in alloimmunized pregnancies, in order to determine whether the fetus is at risk of fetal erythroblastosis or not. The sensitivity and specificity of this examination in our conditions reaches 99-100%.
We perform this examination from the 10th week of pregnancy from 10 ml of non-coagulating peripheral blood collected in EDTA. This examination is fully covered by the insurance company.
We recommend indicating this test especially in alloimmunized pregnancies, preferably before the 20th week of pregnancy, before a more massive transplacental transfer of anti-D IgG antibodies from the maternal periphery to the fetal circulation due to FcRn (neonatal Fc receptor) expression on placental trophoblasts. FcRn actively binds the Fc portion of the parent IgG molecule and mediates its transfer across the placenta.
The only restriction for indicating physicians is that the mother's peripheral blood must be processed in the laboratory no later than 24 hours after collection. If the fetus is RhD negative, it is not at risk of maternal alloimmunization.