Maternal screening

Maternal screening tests measure the levels and concentrations of different proteins and hormones in the mother’s blood; the tests can be used to assess the risk of complications during the pregnancy. There are many different tests which may be carried out; and they are often carried out at different times during the pregnancy. Some of the tests include:

  • AFP (alpha fetoprotein): this is a protein which is produced by the foetus; it reaches the mother’s blood via the placenta. Levels of AFP increase during the first half of the pregnancy.
  • Human chorionic gonadotrophin (hCG): this is a hormone, which is produced in the placenta. Levels rise during the early stage of pregnancy and then start to fall.
  • Unconjugated oestriol (ue3): this is a hormone, which is produced by both the placenta and the foetus.
  • Pregnancy associated plasma protein A (PAPP-A): this is a hormone, which is produced by the placenta; levels usually rise during the first half of pregnancy and then start to decline.

When is the test used?

The screening tests are used to test for Down’s syndrome and spina bifida. The results of the tests can be used to calculate the risk of a mother having a baby with either a birth defect or an inherited condition, such as Down’s syndrome (not all defects and conditions can be diagnosed during pregnancy).

The results of the test are combined to allow doctors to determine the risk of a baby being born with an inherited condition. The risk of Down’s syndrome is considered in the context of the mother’s age and body weight.

The tests are carried out as routine procedure for pregnant women in the UK; however, women are not obliged to have the test.

How is the test done?

The tests are carried out by taking a sample of the mother’s blood; a needle is inserted into a vein in the arm and the blood is collected in a syringe. The sample is then bottled, labelled and sent off for analysis; all the tests can be done from the same sample of blood.

What do the test results show?

The test results will be interpreted and explained by a doctor or midwife; if necessary, a genetic counsellor will also be on hand to offer advice and support.

If levels of AFP are lower than normal, this may indicate a higher risk of Down’s syndrome. If levels of AFP are higher than normal, this may indicate that the baby has a neural tube defect, such as spina bifida.

If the level of hCG is higher than normal, this may indicate a higher risk of Down’s syndrome.

The oestriol level is usually lower than normal when the baby is affected by Down’s syndrome (the test is usually carried out at 16 weeks).

When a PAPP-A test is carried out before 13 weeks, levels tend to be lower than normal in mothers who are having a baby with Down’s syndrome.

The results of the screening tests are a guide and should not be taken as fact; the doctor or midwife will explain the results to the patient and discuss the options and possible outcomes.

Specific Blood Tests

Blood Test Guide

Medic8® Guides

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