can I find out the sex at 17 weeks?

[nnbb]

I had a doctors apt today and due to some cramping i've been having he decided to move my 20 week ultrasound to next week. I will be 17 weeks and 1 day, He said that I shouldn't have to have another unless there is a problem and that everything will be the same at 17 weeks as 20 for what they are looking for, so will they still be able to tell me the sex ? I hope so cause I have to know what I'm having I can't wait,