A new antenatal screening test for Down's syndrome is now available in Britain. The integrated test combines blood tests and an ultrasound scan to produce a single estimate of the woman's risk of having a child with Down's syndrome.

The new test uses a woman's age, two measurements taken between 10 and 13 weeks of pregnancy (a nuchal translucency ultrasound measurement of the fetus and the level of pregnancy associated plasma protein A in the woman's blood), and the measurement of four substances in the woman's blood taken two to four weeks later (a fetoprotein, …