I found out at 15 weeks. The tech could clearly see them both. And at my next appt at 19 weeks, she confirmed that it was still a boy and a girl. :)
At my 17 week u/s the tech was pretty sure 1 of my twins was a girl and she said maybe the other was a boy. I found out at my 19 week u/s that both babies are definitely boys. So they can sometimes tell but sometimes it is still too early to be 100% sure.
Yes, but make sure they get a clear veiw. I have twins and they told me that they thought baby b was a girl when i was 16 weeks but at 18 weeks he was clearly a boy. They got my hopes up for a girl and a boy, it was a little depressing for me when I found out I wasn't having a girl.
Pretty good chance of learning the gender of at least one of your babies at 16 weeks! Congratulations!!!