Hi 12 weeks is optimal. You can have the blood test part earlier, though. It depends on where you live, where you go, and your circumstances, whether you are out of pocket. In Sydney, it depends on who you go through whether it is a routine test or not. A lot of places only recommend it for those over 35. Other places, it's just a regular referral. It was going to cost me well over $100 in Sydney, but I insisted to a doctor that I should be referred to a place in Manly, as they bulk-billed me when I was pregnant with my first. So, that worked out. In Melbourne, I'm not sure if it is routine or not....I believe in most cases, it is. My sister is 23 years old and having it, so I assume most people do. I'll ask her whether it's costing her anything. I was never worried about the results, and didn't even have the blood test part, I just wanted to see my baby! The 12 week scan is simply amazing.