FetalRHDgenotyping in maternal serum during the first trimester of pregnancy

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Abstract
Summary. FetalRHDgenotype determination is useful in the management of sensitized RhD‐negative pregnant women. It can be ascertained early during pregnancy by chorionic villus sampling (CVS) or amniocentesis. However, these procedures are invasive, resulting both in an increased risk of fetal loss and in an increased severity of immunization due to fetomaternal haemorrhage. A reliable determination ofRHDgenotype by fetal DNA analysis in maternal serum during the first trimester of pregnancy is reported in this study. One hundred and six sera from RhD‐negative pregnant women were obtained during the first trimester of pregnancy. These sera were tested for the presence ofRHDgene using a new real‐time polymerase chain reaction assay and the results compared with those obtained later in pregnancy on amniotic fluid cells and byRHDserology of the new‐born. All sera from women carrying a RhD‐positive fetus (n = 62) gave positive results forRHDgene detection and sera from women carrying a RhD‐negative fetus (n = 40) were negative. The high level of accuracy of fetalRHDgenotyping obtained in this study could enable this technique to be offered on a routine basis for the management of RhD‐negative patients during the first trimester of pregnancy.