Checks could be done early in pregnancy
A four-stage test is far more effective at detecting Down's syndrome than standard tests, researchers have found.
They have found the test, plus maternal age, is more accurate than age alone.
And carrying out the quadruple blood test is also more effective than a double or triple test, the team from Barts and The London School of Medicine and Dentistry found.
It is a better indicator of which women should be offered further tests, such as amniocentesis which carries a risk of miscarriage, to confirm the diagnosis.
The quadruple test is used across the world, but is not the standard test offered in the UK.
Department of Health guidance says pregnant women should be offered at least a double blood test.
The research team say some women are offered the quadruple test, but many women miss out, despite it costing little more than the double test.
One in every 700 babies born in the UK has a extra slice of genetic material which means they are born with Down's syndrome.
It causes degrees of mental disability, and sometimes heart defects and hearing and sight problems.
Most women are screened for Down's at between 14 and 22 weeks of pregnancy.
Researchers from Barts antenatal did blood screening for Down's syndrome with the quadruple test in around 46,000 pregnancies from 14 UK hospitals between 1996 and 2001.
The quadruple test looks for levels of four markers for Down's syndrome in mother's blood.
Low levels of alphafetoprotein and unconjugated oestriol and high levels of human chorionic gonadotropin and inhibin indicate Down's syndrome.
Eighty-eight women had Down's syndrome pregnancies.
The quadruple test detected 81% (77) of the pregnancies.
Those whose tests suggested Down's were offered an amniocentesis or chorionic villus sampling to confirm the diagnosis.
The detection rate using maternal age alone, using a cut-off age of 35, was 51%.
The quadruple test had a 7% false-positive rate, compared to 14% using age alone.
The quadruple test was also better than screening reliant on the measurement of two or three blood markers.
The research is published in The Lancet.
'Test of choice'
Professor Nicholas Wald, who led the research, told BBC News Online: "There is no real impediment to offering the quadruple test.
"It could be done in any laboratory that already tests for Down's.
"There is perhaps not sufficient recognition of the advantages of the test, and even when there is, there's a need for resources."
"Our results, from a routine screening service, confirm the value of early second trimester serum screening over screening by use of maternal age alone, in contradiction to recent opinion, and lend support to the decision of the UK government to offer serum screening to all pregnant women.
"We have also confirmed that in the second trimester the quadruple test is sufficiently more effective than the double or triple tests that it should be regarded as the test of choice at this time of pregnancy."
Writing in the Lancet, Peter Benn of the University of Connecticut, US, said: "This report further supports the team's 1988 recommendation that serum-screening replace advanced maternal age as the primary screen for Down's syndrome in the second trimester.
"Use of maternal age as a primary criterion for offering amniocentesis results in very high rates of this invasive testing and is a suboptimum use of resources."
He added: "Policy advisory groups in other countries should follow the UK initiative and abandon obsolete guidelines that have advocated offering amniocentesis to all women aged 35, or more, without routinely incorporating serum and ultrasound screening into their risk assessment."