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Pregnancy - Antenatal tests and screening

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Antenatal care involves monitoring the health of you and your baby throughout pregnancy until the birth. You'll be offered various tests and scans, and you can decide whether or not to have them.

During routine antenatal care, the midwife or doctor will check your blood pressure, blood type, urine and general health. They'll also offer you the following tests and screening.

Ultrasound scans

These use high-frequency soundwaves to create a picture of your baby on a screen. The person doing the scan (sonographer) will spread gel on your stomach, and move a hand-held unit around on it. 

The number and timing of scans varies, but most  pregnant women are offered two.

  • The dating scan. This is offered between eight and 14 weeks of pregnancy. It checks that the baby is alive and well, and has grown to the expected size in relation to how long you've been pregnant. It also checks to see if you're having twins. Most women are offered this early scan, but it depends on where you live.
  • The anomaly scan. This is offered between 18 and 20 weeks of pregnancy. It checks that the baby is growing well, and looks at the baby's limbs, face, head and brain structures, and major organs, including the heart, lungs, bladder, kidneys and bowel.

    The anomaly scan will detect serious problems, but it can't guarantee that the baby is normal. Routine scans can't detect some heart defects, for example. You'll be able to see the baby, and you may be offered a photograph of it to keep. At most NHS units, you'll be charged for this photo.  

    If any abnormalities are found, the doctors will explain these, and they might arrange further tests to make a definite diagnosis. The charity Antenatal Results and Choices can offer information and support. See Useful links.

Tests for Down's syndrome

These tests are offered to all pregnant women, regardless of age (the risk of Down's syndrome increases with age).

Some mothers choose to go through pregnancy without screening. It's important to consider what it would mean to you if the test showed an increased chance of your baby having Down's syndrome. It can help to discuss your personal circumstances with the midwife and the people close to you.

The screening tests are:

  • Nuchal translucency
    This is a special ultrasound test, carried out at 11 to 13 weeks, which measures the amount of fluid at the back of the baby's neck. The amount is used to work out the possibility of Down's syndrome.
  • Combined screening test
    Scans may be combined with a blood test that measures two chemicals that are associated  with pregnancy. Information from the scan and blood test is used to calculate the chance of Down's syndrome occurring.
  • Serum screening
    This is a blood test that screens for Down's syndrome, usually at around 16 weeks of pregnancy. It measures three or four pregnancy-associated chemicals to assess your chances of having a baby with Down's syndrome. Serum screening is not used in pregnancies with twins, triplets or more.  

Tests that measure the possibility of Down's syndrome don't give a definite answer. If your result shows that your baby has a high chance of having Down's syndrome, you'll be offered a diagnostic test. This will be either:

  • Chorionic villus sampling (CVS)
    This test is offered at about 11 to 13 weeks. The doctor obtains a sample of the placenta for testing, either by passing a thin needle through the wall of the abdomen, or by passing a small tube through the vagina and the neck of the womb (cervix).

    CVS carries a 1-2% risk of miscarriage (one to two women out of every 100 who have CVS will miscarry). The preliminary results should be ready in two to three days, and confirmed within two weeks.
  • Amniocentesis
    This test can be offered after 15 weeks of pregnancy. Using ultrasound as a guide, a sample of the fluid surrounding the baby is extracted using a needle that's inserted through your abdomen. The cells from this fluid are then examined for chromosome disorders, including Down's syndrome.

    There's a 0.5-1% risk of miscarriage as a result of the test (up to one woman in every 100 who has an amniocentesis will have a miscarriage). The results should be available within three working days, but if all the chromosomes have to be looked at, it can take up to three weeks.

For more information on antenatal screening, and on what it means if the results are positive, see Useful links. You can also talk to your midwife or doctor at any time.

Watch the video

Antenatal screening helps you manage your pregnancy better and lets you know how your baby is progressing. Two mums talk about what screening involves. 

Medical Review: May 25, 2009

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