TY - JOUR T1 - Cell-free fetal DNA and non-invasive prenatal diagnosis JF - British Journal of General Practice JO - Br J Gen Pract SP - e146 LP - e148 DO - 10.3399/bjgp09X420572 VL - 59 IS - 562 AU - Imran Rafi AU - Lyn Chitty Y1 - 2009/05/01 UR - http://bjgp.org/content/59/562/e146.abstract N2 - Currently in the UK, prenatal diagnosis of genetic conditions and Down's syndrome requires invasive diagnostic tests such as amniocentesis and chorionic villus sampling (CVS). Procedural related miscarriage rates of about 1% have been quoted for these tests which are not usually done before 11 weeks' gestation.1 Annually in the UK, 32 000 women have an invasive diagnostic test as a result of other screening tests, indicating that they are at increased risk for their children having Down's syndrome. Around a further 1500 pregnant women have an invasive test because the fetus is at high risk of a genetic condition.An area that has generated much interest in recent years has been in isolating fetal genetic material present in maternal blood as a target for non-invasive prenatal diagnosis (NIPD). In 1997 Lo et al2 identified cell-free fetal DNA in the maternal circulation. This finding has generated research in the development of clinical applications based on analysing this fetal genetic material for NIPD. Cell-free fetal DNA represents extracellular DNA which originates from trophoblastic cells.3 However, the vast majority of cell-free DNA in maternal blood originates from the mother, with cell-free fetal DNA representing only 3% of the total cell-free circulating DNA in early pregnancy rising to 6% in late pregnancy.4After delivery, cell-free fetal DNA is rapidly cleared from the maternal circulation, making it specific to that pregnancy. As the fetal DNA is swamped by the presence of cell-free maternal DNA, the challenge has been to separate the fetal from the maternal cell-free DNA. Various methods have been used for this, including using methods based on the fact that the fetal DNA is shorter than maternal DNA. However, it is still not possible to extract pure fetal DNA and so currently prenatal diagnosis using cell-free fetal DNA is … ER -