Pregnancy

INVASIVE PRENATAL TESTS: CHORION VILLUS SAMPLING & AMNIOCENTESIS

These are diagnostic tests.

The commonest indication for these tests is to check the baby’s chromosomes, but may be used to diagnose inherited conditions such as cystic fibrosis, Tay-Sachs, sickle cell or haemophilia.

CHORION VILLUS SAMPLING (11-15 WEEKS)

A thin needle is passed through the abdomen to sample the placenta (afterbirth). Both baby and placenta develop from the same cells, therefore the chromosomes present in the placenta can be used to check the chromosomes in the baby.

CVS is not performed before 11 weeks. The procedure takes less than two minutes and is performed under scan guidance.

AMNIOCENTESIS

A fine needle is passed through the abdomen and amniotic fluid around the baby is taken and tested for abnormalities.

Amniocentesis is not performed before 15 weeks. The procedure is very quick and takes less than two minutes and is performed under scan guidance.

RESULTS

A preliminary result is available in 3 days and the final result within 1-2 weeks.

RISKS

The extra risk of miscarriage associated with these tests is 1%. In approximately 1:1000 cases the test will need to be repeated because the cells will not grow in the laboratory or the results are inconclusive.

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