Tests & Ultrasounds

So my doctor said i only get two ultrasounds. One on my first visit (9.4 weeks) and one at 20 weeks. My husband and I have decided to get the tests done for any abnormalities, especially the NT test. They are doing these tests on my next visit (the 20th of this month. 16.4weeks). It just occurred to me, they have to do the NT test with am ultrasound. Does that mean that they won't do the test until 20 weeks, or that they will do an ultrasound this apt with the other tests