During amniocentesis, approximately 15mls of amniotic fluid is withdrawn from the amniotic sac.  Amniotic fluid contains cells that have been shed from the fetus.

It involves passing a fine needle through your abdomen into the uterus in order to aspirate the amniotic fluid.

An amniocentesis is usually performed around 15 – 16 weeks of gestation, always with ultrasound guidance.

Although performed safely, there is a small risk of miscarriage from an amniocentesis (less than 1:300).

Preliminary results for Down syndrome can be available within 3 – 4 days.  The full chromosome analysis takes between 2 and 2 1/2 weeks.