Does anyone know how often they can tell the sex of the baby at the 18-20 week u/s? And does anyone else know how often they get it wrong? As this is wll be my first baby we need to buy EVERYTHING & I'd love to get a head start in the sales that are on right now but I don't want to start shopping if I don't know what we are having.

Also, when is normal to have the 18/20 week u/s? I always thought it was at 18 weeks but a lot of girls on heere talk about 20 week u/s