nub theory

[noorey]

what is the basic trick of nub theory

That a foetus of around 12wks has a 'nub' that will eventually turn into genitalia and if it points up then its likely a boy and if it points down then its likely a girl.

An experienced sonographer with a good view can accurately tell the sex of a c.12wk foetus with fairly good accuracy (around 75% if I remember rightly).