No, they didn't ask me at 12 weeks either, 20 weeks must be when they schedule that one for. In fact, at my 12 week scan all talks with the midwife were held in the corridor in front of other waiting patients, not very confidential!
I also read of some hospitals not letting fathers into the scan until abnormalities have been ruled out, because sometimes they've highlighted an abnormality that is genetic, only to find out that it doesn't run in the father's family and it turns out that the father is not the bio dad and he didn't know that was a possibility. So by doing all that without the father present, the mother has the choice about what to say to her partner. I don't think most places do that though. I haven't heard of it happening in my area and I'd be quite put out if my partner couldn't come in to the actual scan as she's female and therefore we've blatantly used donor sperm!