At my 20 week scan I didn't find out the sex of DC2 but I was told I had a left-lateral placenta.
I googled this because I'd heard that babies tend to face the placenta and was worried about a back-to-back labour.
Found nothing on left lateral placentas really except for a link to one study which linked placenta position & gender. Apparently it means I'm have a girl and the accuracy was something like 99%.
There are whole websites set up to talk about stuff like this.
IMO if the placenta thing were true then sonographers wouldn't spend ages looking for genitals in babies who have their legs crossed etc. They wouldn't need to would they?
DC2 due in 3 weeks so no idea if I am having a girl but it's got a 1:2 chance of being right 