A/S question??

kseav

I have seen that many of you are finding out at 1516 weeks and the post a couple below at 14 weeks knowing the sex. I simply asked to have my scan at 17w5d so neither DH and I would have to change work schedules right before we leave for 2 weeks vaca. I was told no and my window was 18 to 20 weeks?!?! Any reason why??