What will the test tell me?
An AFP blood test (also known as a 'maternal serum alpha-fetoprotein' or 'MSAFP') is used to assess the likelihood that a pregnant woman's baby will have a 'neural tube defect' (or NTD). Neural tube defects occur when there are problems with the development of the baby's brain, skull and spinal cord very early in the pregnancy. The defect causes part of the baby's spinal cord to be exposed (called 'spina bifida'), or the baby's brain fails to grow (called 'anencephaly'). People born with spina bifida can have various levels of brain damage and often a weakness or paralysis of their legs. However, they often lead very full and active lives. Babies born with anencephaly cannot survive outside the womb and die soon after birth.
Any woman of any age can have a baby with a neural tube defect. Having adequate folic acid intakes during the first 12 weeks of pregnancy can reduce the likelihood of having a baby with a neural tube defect by up to 70%. You can read more about folic acid supplements and neural tube defects in
class A.
What will the test tell me?
An AFP is done by taking a blood sample at 16 weeks of pregnancy (but can be taken between 16 and 18 weeks). Tests after 18 weeks cannot be relied upon. The accuracy of the test very much depends on the unborn baby's age being calculated correctly. This may be reliably calculated if the woman has regular periods and is sure of the date of her last menstrual period, or if she has had an earlier dating ultrasound. Sometimes an ultrasound is scheduled at around the same time of the AFP blood test.
An AFP is a 'screening test'. It aims to identify babies that may be at increased 'risk' (or have a higher chance) of having a neural tube defect, but it cannot definitely tell if the baby has the defect. The AFP test is about 90% accurate. This means that around 10% of babies with a neural tube defect will be missed. The test also has a high 'false positive result'.