I'm currently investigating the 'skull theory' which suggests unique structural formation of both the female and male skull. Here is an article which goes into more detail

http://www.juniordentist.com/differentiate-male-skull-female-skull.html

 

I would appreciate your opinion regarding the possible gender of the foetus pictured in this 20 week ultrasound

 

 

 

 

 

Its very hard to tell but it looks like a boy to me. Do keep us posted.