hey there sakoon
The down syndrome test is a two part test.
Firstly at about 10 weeks they take a blood test from you. They also take blood from you at this stage to check your iron, anti-bodies for things like german measals, and also your blood group.

Then at your 12 week ultrasound they check the thickness of the skin on the back of your baby's neck. Anything under 3mm is great.

Both these results are they faxed through to the Murdoch Institute. They then combine both these results and give you a reading based on the blood results, u/sound and your age, what your risk for having a downs baby.

It does not harm the baby as they are done when you would usually have other testing. The choice is up to you if you do it or not- there is a charge for it. Around $70 for bloods on top of the bulk billing charge, and the u/sound clinics charge.

Its up to you if you do it or not.
good luck
odette