Extending non-invasive prenatal testing to non-invasive prenatal diagnosis

Molecular prenatal diagnosis of genetic conditions has historically required invasive procedures to obtain a sample of tissue from a developing pregnancy—either from the placenta (chorionic villus sampling) or from the amniotic fluid (amniocentesis). Both have a small risk of causing a miscarriage, and the earliest point at which testing can be undertaken is 11 weeks into a pregnancy (for CVS). Non-invasive prenatal testing (NIPT) is an exciting step forward in prenatal genetic diagnosis, whereby fetal DNA can be obtained and tested by taking blood samples from a pregnant mother. This avoids the miscarriage risk associated with invasive prenatal tests and can also be performed at an earlier stage of gestation. The paper by Duan et al 1 demonstrates the great potential benefits of this new technology for families affected by genetic conditions. The presence of cell-free fetal DNA in maternal blood was demonstrated in 1997 by Lo  et al , who showed that Y-chromosome-derived sequences were present in serum samples from women pregnant with male fetuses. This cell-free fetal DNA is derived from the placenta: it has placental epigenetic signatures and is present in anembryonic pregnancies. Cell-free fetal DNA fragments are shorter than background maternally derived free DNA fragments, and the concentration of fetal DNA in maternal serum rises as a pregnancy advances.2 NIPT exploits the presence of cell-free fetal DNA to allow genetic testing of fetal material without the need for an invasive procedure. From the first study that showed the potential to establish fetal sex by detecting Y-chromosome-derived sequences, later studies went on to …