Does anyone know about blood to determine the gender??

So I'm in the Air Force and I go to a doctor assigned by them. I asked if they did the blood test to determine the gender and they said that they didn't do that😕. Does anyone know if I can get it done somewhere else, I know SneakPeek is an option but I've seen the reviews and would like something more accurate done. I'm not really allowed to go anywhere else without a referral and I'm sure she wouldn't write me one just because they don't offer the test there.