I had my amnio done at 16 weeks, they want the baby to be big enough so it cannot go into this area which is on the lower left side of your stomach, that is where the needle is inserted. Then you have to wait about 2 weeks for the test results.
Good Luck To You,
16 weeks is about the earliest a dr can extract enough amnio to test. I had one at 15.5 weeks and it took three insertions to finally get some fluid. That, in my opionion, was because it was just a tad too early.