Prenatal Diagnosis of Fetal RhD Status by molecular analysis of maternal Plasma,
YMD Lo, et al (Chinese Univ of Hong Kong, China; John Radcliffe Hosp, Oxford, England).
N Engl J Med 339: 1734-1738, 1998.
The rhesus (Rh) blood group system is involved in the hemolytic disease of the newborn. In cases in which the mother is RhD negative and the father heterozygous, there is a 50% chance that the child will be Rh positive. Several groups have analysed the possibility of determining the fetal RhD status from the fetal cells isolated from the maternal circulation. The feasibility of the RhD genotyping from fetal DNA extracted from maternal plasma samples was investigated.
It is possible to run a batch of samples to completion, allowing detection of as little DNA as is present in 1 fetal red cell, in 2 hours. In 39 cases where Rh-negative gravidas bore Rh-positive fetuses, detection of the Rh-positive DNA segments derived from the fetus was possible in all 37 pregnancies past 9 weeks of gestation. This is a rapid, highly accurate, sensitive method of detecting an Rh-positive fetus in this sensitized Rh negative woman, given the heterozygous Rh positive father. The determination can be made as early as the second trimester of pregnancy, and intrapartum RhoGam administration to such a woman can then be employed rationally.