How is an amniocentesis done?
What will results tell me?
Risks and problems associated with amniocentesis
Early amniocentesis (less than 15 weeks)
Amnio vs CVS
An amniocentesis (or 'amnio') is a test that takes a sample of amniotic fluid that the baby floats in from inside the woman's uterus. The fluid has cells floating in it that have been naturally shed from the baby. The sample of amniotic fluid is then sent to the laboratory to 'grow' or 'culture' the cells, until there are enough to be used to 'map' the baby's genes or chromosomes. An amniocentesis aims to identify the presence of a genetic disorder (such as Down syndrome) or other inherited disorders such as muscular dystrophy or
cystic fibrosis. Even though amniocentesis is thought to be fairly accurate (up to 99%), not all birth defects and health problems can be detected with this procedure.
An amniocentesis is usually performed at about 15 weeks of pregnancy, but can be performed up to 18 weeks or even later than this. Amniocentesis is occasionally used during very late pregnancy for other medical reasons, such as checking the lung maturity of a baby when the caregiver is considering inducing the labour prematurely. Amniocentesis can also be performed earlier than 15 weeks, but may involve more complications. This is discussed below in
early amniocentesis.
How is a amniocentesis done?
An amniocentesis is performed by the doctor inserting a needle through the woman's abdomen into the uterus (known as 'transabdominal' or 'TA') to where a pool of fluid surrounding the baby is. An ultrasound is also done (with the transducer placed on the woman's abdomen) to create an image of the baby and placenta and help guide the doctor to take the fluid from the correct place, avoiding the baby and the placenta. The needle often has to be manoeuvred several times to obtain the fluid required. Sometimes more than one needle insertion is needed in order to collect enough fluid.