Check with the midwife and also at the u/s place as they should know when the best time to measure the Nuchal fold.
My u/s will just be done in my OB's office. So I'll just ring back and ask them to check.

It's just that the OB and midwife did not tell me which date to book in for. They just said in a few weeks. So when I went to the receptionist to pay I just told her I had to book in for my next u/s and she just picked any old date!