Ultrasound determination test?

I had my 20 week ultrasound yesterday and the tech said that in some cases it is hard to hide (like when the parents don't want to know) so I guess that means in some cases it's not as easy to tell. But we saw clear as anything that it was a boy; there really was absolutely no doubt because he was not shy at all and they had an angle where it was just obvious as anything. =) Overall I guess it depends on what kind of pictures they get, but if they told you it's a boy then it's most likely a boy. I remember going with my sister to hers and they said they were pretty sure it was a girl but not 100%, and it was indeed a girl. I don't remember what week she was at for that one though. The ultrasound techs aren't likely to mistake it if they see a though. They know exactly what's in there, what's an umbilical cord, what's a kidney and what's a stomach, etc... they usually are really good with identifying everything in there!