Pregnancy - Screening Tests

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What are screening tests?

A screening test aims to detect a disease or condition in the early stages before it causes significant problems, and where treatment can be offered. The potential benefits of a screening test should outweigh any possible risks from the test.

This leaflet lists routine screening tests which should be offered to all pregnant women in the UK. Most pregnant women have normal test results. A small number of tests are abnormal. In these cases further assessment and/or treatment can be offered which may prevent serious problems.

(Various other tests may also be offered in certain circumstances during pregnancy. For example, if you have symptoms which suggest a complication then other tests may be relevant. These are not discussed further.)

A midwife or doctor should discuss each test with you before it is done. You need to agree for the tests to be done. You can refuse to have a test if you do not want it.

General history (talking to your doctor or midwife)

Early on in your pregnancy your doctor or midwife will ask various questions about your general health, family history, social history, and about any previous pregnancies which you have had. Strictly speaking, this is not a 'test'. However, it can raise issues which may need special attention during the pregnancy which may prevent problems later in the pregnancy.

For example, if you have diabetes, or if you had pre-eclampsia in a previous pregnancy, you will need closer monitoring than usual during the pregnancy. If you have social or family problems such as domestic violence then you may need special help.

Routine physical examinations

• Weight and height. Early on in the pregnancy your doctor or midwife will check your weight and height. This is to see if you are significantly underweight or overweight which may increase the risk of developing problems during pregnancy. Usually, after then your weight or height need not be measured again during pregnancy.
   
• Assessing the growth of the baby. This is done by by a midwife or doctor during routine antenatal checks. They use a tape to measure from the top of the growing uterus (womb) to the pubic bone (the bone at the bottom of your abdomen).
   
• Blood pressure. This is measured regularly during routine antenatal checks. (Together with a urine test which detects for protein, this screens for a complication of pregnancy called pre-eclampsia. See separate leaflet called 'Pre-eclampsia' for details.)
   
• Examination of the baby's position. About 36 weeks of pregnancy a doctor or midwife will examine your abdomen to feel the baby to detect if the baby is lying breech (bottom down). If so, treatment to turn the baby to a head down position may be considered.

If you are otherwise healthy, other physical examinations are not routinely done. For example, routine vaginal or breast examinations used to be done in the past, but are not neccessary. (They may be done if you have symptoms or problems which warrant examination.)

Routine urine tests

Urine is checked at antenatal checks using a simple dipstick test to detect:

• Protein. Protein in the urine may indicate early pre-eclampsia.
   
• Bacteria (germs). During pregnancy you can have an infection of the urine without symptoms ('asymptomatic bacteruria'). This can increase the risk of problems later in pregnancy such as early childbirth. It can be treated with antibiotics.

Routine blood tests

A sample of blood is taken early on in pregnancy and put into several tubes. These are sent to the lab to check for:

• Anaemia. The common reason for anaemia is lack of iron which can usually be treated easily with iron tablets.
   
• Blood group including rhesus D status and red cell antibodies. If you are rhesus D negative and your baby is rhesus positive then you may form anti-D antibodies in your bloodstream. These are not dangerous in the first pregnancy, but can attack the blood cells of a baby who is rhesus D positive in any future pregnancy. To prevent this you will usually be offered anti-D injections later in the pregnancy. Various other antibodies sometimes develop against red cells. Their significance varies and a doctor or midwife will explain if any action should be taken if they are detected.
   
• Rubella status. This test checks for antibodies to the rubella virus (german measles). If antibodies are present it means that you are immune to this infection. If you are not immune, when you are pregnant you should keep away from anyone who may have rubella. Also, consider being immunised against rubella after giving birth to protect future pregnancies. (If a pregnant mother develops rubella it can seriously damage the unborn baby. Ideally, your rubella status should be checked before becoming pregnant so that, if necessary, you can be immunised before becoming pregnant.)
   
• Certain infections. Some uncommon but serious infections are checked for. These are:
  • HIV. This is the virus that causes AIDS. You can be infected with HIV for years before it causes symptoms. The risk of passing this virus on to your baby can be greatly reduced with treatment during pregnancy, and delivery by caesarean section.
  • Hepatitis B. Many people are carriers of this virus but have no symptoms. In some cases it can cause serious liver damage. If you have this virus, it may be prevented from affecting your baby if the baby is immunised at birth.
  • Syphilis. This is an uncommon sexually transmitted infection. Again, you can be infected with this bacteria without realising and pass it on to your baby. It can develop into a serious illness. It can be treated with antibiotics.

A repeat blood test at about 28 weeks is usually offered to re-check for anaemia and red cell antibodies.

Routine ultrasound scans

An ultrasound scan is a safe and painless test which uses sound waves to create images of structures inside your body such as an unborn baby. A routine ultrasound scan is usually offered at:

• 10-13 weeks of pregnancy to accurately date the age of the unborn baby and expected time of birth, and to check for twins (or more), and at:
• 18-20 weeks of pregnancy to look for physical abnormalities of the unborn baby.

Screening for Down's syndrome

Down's syndrome is a condition which is caused by an abnormal chromosome. Children with Down's syndrome have learning disability and often have other medical problems. There are different screening tests for Down's syndrome and so different tests may be used in different areas. They include a blood test and a special ultrasound test, or both. Screening for Down's syndrome is offered sometime between 11 and 20 weeks of pregnancy, depending on the type of test used.

Your doctor or midwife will explain the type of test performed in your area, and the implications of the results. For example, some women opt for termination of pregnancy if they are found to have a Down's syndrome child. Note: the screening test is not a clear-cut diagnostic test. Therefore:

• A 'positive' test means that you may have a child with Down's syndrome. If you have a positive screening test, further tests are needed to confirm the diagnosis. In some positive tests the baby does not have Down's syndrome (a 'false positive' result).
• A negative test does not completely rule out Down's syndrome. (That is, in some cases there is a 'false negative' result.) Currently the screening tests identify about 60-80 in 100 babies who have Down's syndrome.

You do not have to have a screening test for Down's syndrome if you do not want one.

Screening for placenta previa

Placenta previa means that the placenta is covering the opening from the uterus to the cervix. This can cause serious problems during childbirth. If an earlier ultrasound scan indicates that you may have a placenta previa, a repeat scan at 36 weeks pregnancy may be advised to clarify the position of the placenta before delivery.

A final point

The above tests are the usual routine tests advised for all pregnant women. If you have symptoms or problems which suggest pregnancy complications, various other examinations and tests may be advised. See your midwife or doctor if you have any concerns about your pregnancy, or if you wish to discuss any tests in more detail.

© EMIS and PIP 2004   Updated: July 2004   Review Date: August 2005   CHIQ Accredited

The authors and editors of this article are employed to create accurate and up to date content reflecting reliable research evidence, guidance and best clinical practice. They are free from any commercial conflicts of interest. Find out more about updating.

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