When to do nuchal scan?

I wanted to survey all you pregnant ladies here. After more than a week of trying to get in touch with my OB to get the blood work ordered for genetic testing and voice my concern that my next ultrasound is scheduled too far out (15 weeks) I was told that the nuchal scan and the blood work is not typically done until 16-18 weeks. This is my second baby and that is absolutely not how it was done my first time around. Was curious if anyone else was told this as a simple google search still says the best time to measure nuchal translucency is between 11-14 weeks. I'm currently 11+4 weeks pregnant and concerned because my OB would not reschedule for a sooner date. TIA!