If budget allows, you may consider doing the amniotensis in a private clinic. If you do it in the private clinic, it takes only 1 day for the test result; the earlier you know, the less time you worried. I totally understand the time you wait for the result is very painful coz really you cannot sleep well everyday!
However, bad side is, the cost to do it in the private clinic is super expensive, it costs HK$4,500. :(