Girls if you could help me out for a sec...

I am looking at booking a 3d/4d ultrasound scan today and I need to put down the week when I would like to view to find out the sex of the baby. So much conflicting info on the net. Some same you can at 16 weeks.

I can't wait but what do you think? Or have anyone done it before? Cos it is 3/4d it is possible at 16 weeks to see the sex or would you suggest 18-20 weeks?