Alpha fetoprotein (AFP) and testing for Down's Syndrome in Pregnancy

Screening for Down’s syndrome and other genetic disorders is offered to all pregnant women. Traditionally an Alpha Fetoprotein test was used to measure the levels of AFP in your blood. Where levels were very low, mums were offered a diagnostic test to establish the likelihood of their baby having Down’s syndrome. The AFP test has been replaced by a more accurate screening process and nowadays you will be offered either combined screening or serum screening.

Combined screening, also known as a Nuchal Translucency test, involves a blood test and an ultrasound scan to calculate your chances of having a baby with Down’s syndrome. The blood test measures two blood chemicals associated with pregnancy. And the ultrasound measures the thickness of the nuchal translucency (which is a pocket of fluid) at the back of your baby's neck. This test usually happens between weeks 8-14 of your pregnancy and can be used if you’re expecting more than one baby.

Serum screening usually happens when you’re around 16 weeks pregnant. It measures three or four blood chemicals associated with pregnancy to work out your chances of having a baby with Down’s syndrome. If your test results show an increased risk, you will be offered a diagnosis test, such as chorionic villus sampling (CVS) or amniocentesis – but this doesn’t mean your baby will have Down’s syndrome.

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Glossary

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