TBH I can't quite beleive how they can get it wrong, if they are able to see every other part of the body, to check it's fine, how can they not see the genitals? or internal sexual organs for the baby?
A friend's baby had an ovaric cysts which was spotted during her 20week scan....!!! Admittedly this was at a private clinic, with proper equipment and not the fuzzy machines they have at some NHS hospitals...
In my opinio if they can't be sure about the sex, they can't be sure about much else, and if I didn't have my scan at UCLH Fetal medicine centre, I'd have had a private one as well!!!
Litigation does not have to be an issue, all they have to do is give the disclaimer, I think it's very patronising for hospitals not to sex babies, they do not have to spend hours doing it, but if they see it and the parents wish to know, I cna't understand why shouldn't they tell. And they should be able to explain they can't spend too much time on it.
As far as sex discrimination in some cultures is concerned, I believe in the UK it is only small numbers, and then again, if an unwanted daughter comes to the world, and is neglected and mistreated it's difficult to say whether it an bortion would have been better....