Invasive Prenatal Testing

These tests involve obtaining fetal cells from either the placenta in the case of Chorionic Villus Sampling (CVS) or amniotic fluid in the case of Amniocentesis.

For both tests, rapid results are available within 24-48 hours and longer term results take 10-14 days to be available. Both tests are associated with a minor degree of discomfort. Pain relief is almost never required. Each test generally only requires a few minutes of procedure time.

The test is usually performed to diagnose chromosome abnormality (either following a high risk NIPT result or high risk nuchal translucency) but may occasionally be performed to diagnose uncommon single gene defect disorders or other rare conditions. CVS involves obtaining fetal cells from the placenta either by passing a needle through the abdomen into the placenta or by passing a cannula through the cervix (neck of the womb) to the placenta. Both techniques are performed under ultrasound guidance and the technique performed will depend on technical factors which will be discussed with you by the performing specialist.

The loss rate with CVS is between 0.5 and 1% and in the hands of experienced specialists there is no difference between the two techniques offered. Amniocentesis involves obtaining fetal cells from the amniotic fluid by inserting a needle under ultrasound guidance into the amniotic fluid surrounding the baby. Approximately 20 ml of amniotic fluid is obtained. The miscarriage risk associated with this test is less than 0.5%.