The diagnostic potential of maternal plasma in detecting fetal diseases by DNA test

There is a common perception that fetal blood remains separated from maternal blood until third stage of labor or following abortion, inversion of placenta etc and only IgG can cross the placental barrier due to its small molecular weight. However, recent observations suggest that the placental barrier is not as impermeable as is traditionally known. This is because fetal DNA has been detected in maternal blood as early as 5 weeks.1 Real time quantitative polymerase chain reaction (PCR) is sensitive enough to detect DNA equivalent of a single target cell – a male fetal cell against a background of 12,800 female cells.2 These seminal observations have ushered in a new area of investigations related to Conventionally, DNA based investigations for fetal diseases are done by chorionic villous sampling and amniocentesis. Both are invasive techniques. Recently, molecular diagnosis has also been made possible in early pregnancy from maternal blood which is noninvasive and advantageous. Most of the researches have tried to identify the Y chromosome marker(s) to detect a male fetus and paternally inherited allele. This is currently helpful to detect a very few genetic disorders including Rh D status in Rh negative women in early pregnancy and preeclampsia a few weeks preceding the clinical onset. This is a potential area for prenatal diagnosis in future.