Test: Antenatal Genetic Tests

With regular monitoring and carefully adjusted treatment, both before and during a pregnancy, as well as during the birth, pre-existing conditions can be controlled, and they usually carry little risk for either the mother or the fetus. Any changes in the mother’s condition that may have developed as a result of the pregnancy will normally be reversed soon after the baby has been born.

Chorionic villus sampling

Chorionic villus sampling is usually carried out between the 10th and 13th weeks of pregnancy. Tissue from the edge of the placenta (chorionic villi) is taken and then analysed to look for a chromosomal or genetic abnormality. The risk of miscarriage is increased slightly by having this test.

During the procedure

A small sample of the placenta is taken either by inserting a needle through the abdominal wall or using a flexible tube that is passed through the cervix. Ultrasound is used to guide the tube, and the sample is removed using gentle suction.


Amniocentesis is usually carried out between the 15th and 20th weeks of pregnancy. A small sample of the amniotic fluid surrounding the fetus is removed and analysed for genetic abnormalities. The procedure is associated with a small risk of miscarriage (about 1 in 100 women).

During the procedure

Ultrasound is used to guide a needle into the sac containing the fetus and the amniotic fluid. A small sample of fluid is then withdrawn using a syringe. A slight pricking sensation may be felt.


Chromosome analysis

Samples from genetic tests are analysed to look for a chromosomal abnormality. This test result shows one extra chromosome number 21, indicating Down's syndrome in the fetus.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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