Non-invasive fetal sex determination: impact on clinical practice.

Prenatal fetal sex determination is undertaken in women at high risk of serious genetic disorders affecting a specific sex. Traditionally, this is undertaken by invasive testing, usually chorionic villus sampling, which carries a risk of miscarriage of around 1%. The identification of cell-free fetal DNA in the maternal circulation has allowed the development of 'non-invasive prenatal diagnostic tests', which permit fetal sex determination without risk to the pregnancy.