New US guidelines for Down syndrome screening

The American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant women should be offered screening for Down syndrome, regardless of their age. Lead author Dr Deborah Driscoll said last week that 'this new recommendation says that the maternal age of 35 should no longer be used by itself as a cut-off to determine who is offered screening versus who is offered invasive diagnostic testing'. The advice is published in a Practice Bulletin developed jointly by ACOG and the Society for Maternal-Fetal Medicine, in the January issue of the journal Obstetrics and Gynecology.

Currently, invasive tests such as amniocentesis or CVS (chorionic villus sampling) are only routinely offered to women older than 35, who are at the highest risk of having an affected child. The incidence of Down syndrome is about one in every 1,300 births in young women, rising to one in 350 births for mothers over 35, and one in 25 in those over 45. But since the introduction of screening tests for older women, most children with Down syndrome are now born to younger women, according to Dr Edward McCabe of the Mattel Children's Hospital at the University of California.

The original reason for focussing on women over 35 was that invasive tests carry a small risk of miscarriage - about one in every 200 procedures. According to Dr Nancy Green, medical director of the March of Dimes charity, this risk has declined over the last decade but many women prefer to avoid the test altogether unless they are at high risk of having an affected child. The new guidelines call for all pregnant women to be offered a combination of non-invasive tests during the first trimester. Such tests involve a combination of the 'nuchal translucency' ultrasound method, and a maternal blood test.

Women identified as being at high risk through these initial tests should then be offered either amniocentesis or CVS in the second trimester, say ACOG. Current UK guidelines, issued by the National Institute for Health and Clinical Excellence (NICE) in 2003, already say that all pregnant women should be offered one of a number of proven, non-invasive methods of screening for Down syndrome. Women found to be at high risk of carrying a fetus with Down syndrome are then offered either amniocentesis or CVS.