The test can be performed at about 10 -12 weeks of pregnancy. An ultrasound scan is performed first, to check how far advanced the pregnancy is, and to determine the position of the placenta. There are two ways of performing this test. The test usually takes about 20 to 30 minutes, and can be done in a hospital outpatient department. The woman being tested is awake and aware of what is happening during the test.
Most women describe it as being uncomfortable rather than painful.
Sometimes it is important to know the sex of the fetus and this can be determined very quickly using this test. Identifying a genetic defect can depend on several factors such as the size of the disruption, and therefore how easy it is to find, or whether a sample from an affected relative has been obtained, or how accurate 'Linked genetic markers' are. Your geneticist will discuss all these points with you before any test, and will explain whether there is a risk of error with the test result. As far as the mother's health is concerned, there are thought to be no serious complications, although she should avoid strenuous exercise for a few days. For safety reasons, the test should not be carried out before 10-12 weeks.