Screening tests
Diagnostic tests
New technology
Genetic tests during pregnancy are used to screen for or detect specific inherited disorders in unborn babies. There are many different types of genetic tests available. These range from non-invasive ultrasounds and blood tests called 'screening tests', to more invasive procedures that obtain cells from inside the woman's uterus for examination of the baby's chromosomes (called 'diagnostic tests'. Ultrasounds done at around 18 weeks of pregnancy were the first type of testing done to screen for health disorders and while they can usually detect obvious physical abnormalities (such as kidney and heart defects) they are not able to reveal the actual genetic 'make-up' of a baby (you can read more in
ultrasounds).
Each genetic test has its advantages and disadvantages. Depending on your personal preferences and what is important to you, you are free to choose the test(s) you most prefer, or not to choose any at all. Issues around having genetic counselling, making decisions to accept or decline genetic testing, how to interpret the 'risks' and 'numbers' and some considerations and possible emotional reactions are explored in great depth in
class B.
Screening tests
Screening tests aim to identify babies that may be at increased 'risk' (or have a higher chance) of having a genetic disorder or abnormality. It is important to remember that screening tests only estimate 'risk' and are not 100% accurate. Many women will be estimated as 'high risk', yet their babies will be very healthy and normal. While a few women will be estimated as 'low risk' and yet still carry a baby with a genetic disorder.
Screening tests do not harm the unborn baby and include:
Nuchal Translucency (NT)
AFP blood test
Triple test
Diagnostic tests
Diagnostic tests take a sample of the
placenta or the amniotic fluid from inside the woman's uterus.