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Currently, women, including most of those over 35, considered at risk of having babies with birth defects, such as Down's syndrome, are offered amniocentesis or chorionic villa sampling (CVS) after the third month of pregnancy.
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US scientists have developed a test to predict a risk of Down's syndrome which they claim is 90% accurate.
The test combines a check for two proteins in the blood with ultrasound measurements of the foetus.
Dr Eugene Pergament, professor of obstetrics at Northwestern University in Chicago who led the study, said: "Overall, we may end up with an earlier test, with a higher detection rate, doing less invasive procedures and losing fewer normal pregnancies.
Invasive tests
Currently, women, including most of those over 35, considered at risk of having babies with birth defects, such as Down's syndrome, are offered amniocentesis or chorionic villa sampling (CVS) after the third month of pregnancy.
CVS involves using either a needle inserted through the abdomen or a catheter threaded through the cervix to test the placenta, which nourishes the baby. Amniocentesis uses a needle to sample the amniotic fluid in which the baby floats.
Both are nearly 100% accurate in catching birth defects but carry a slight risk of miscarriage.
Dr Pergament said: "Some women do not undertake CVS or amniocentesis, even if they are at increased reproductive risk for a conception with a genetic disorder, because of their unwillingness to risk loss of the pregnancy."
There is a blood test available after the third month of pregnancy, but it is only 60% accurate for Down's syndrome.
But the recently developed test makes it possible to screen for Down's syndrome in the first three months of pregnancy by looking for two proteins in the blood of pregnant women.
One protein, human chorionic gonadotrophin (free b hCG) is found at high levels and another, pregnancy-associated plasma protein A (papp-A), is at low concentrations when the baby has Down's syndrome.
Ultrasound can also be used to detect symptoms of Down's syndrome, which causes excess skin on the neck of foetuses.
Researchers are now doing a study to see if combining the three tests can provide an earlier, less-invasive test for Down's syndrome.
Down's syndrome is a congenital condition characterised by abnormal chromosomes and mental deficiency.