Double testing
Double testing measures a combination of a protein and a hormone in the mother's blood to screen for birth defects, such as Down's syndrome.
The double test is performed in early pregnancy (second trimester) and measures the levels of one protein (alpha-fetoprotein) and one hormone (human chorionic gonadotropin). The double test also takes into account the mother's age, medical and family history.
As only two markers for Down's syndrome are measured, a triple test or especially a quadruple test are considered more accurate, but they are not offered everywhere in the UK.
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