I've replied to your other thread, but thought I'd answer this one too ...
I'm 38 and our baby is due in Jan. We were offered the nuchal test when we had the 12 wk scan. We decided to have it. At my age, the risk was automatically put at 1:250. After the scan, the sonographer inputted the nuchal results and the risk was adjusted to 1:350. She told us this was still borderline high risk, and we could have a blood test if we wanted to. We went ahead. Along with the blood test was a questionnaire, asking all sorts of questions - even down to the brand of folic acid I was taking. I was pretty shocked to get a phone call a couple of days later, telling me the blood test results put us at a risk of 1:80 for chromosonal defects.
We were given the option of
1) doing nothing
2) waiting for the anomoly scan to look for soft markers
3) having an amnio
Now obviously, the amnio comes with a small risk of miscarriage. They say it's 1%, but these days the risks are actually much smaller. We chewed it over for a few days, and decided to go for amnio. We thought that knowledge brings power, so even if we were expecting a baby with Downs, we could be prepared for it. Also, and more importantly, the tests check for Edwards Syndrome, which is much more severe.
We had the amnio when we were 14 wks pregnant. The build up, and thought of it was much worse than the actual procedure. Of course, I was terrified for a few days afterwards, in case something would go wrong, but nothing did.
The tests our hospital do with the amniotic fluid are completed in a few days, and give a definitive answer. We got a letter to say our baby has no chromosonal defects at all. Which was such a relief.
Of course, the decision is ultimately yours and OHs. Personally I had to have the test. I wouldn't have been able to get through the rest of the pregnancy wondering 'what if' without driving myself demented. And I figured that if we were going to have a Downs Syndrome baby, I could at least do research, and get as prepared as I could be.