I knew retrospectively, too. These twins are my second pregnancy, and for them my first trimester symptoms arrived SO early and were SO strong--just crazy hunger, thirst, and fatigue. When we had our ultrasound, there was a definite feeling of "Oh, so THAT'S why I've been feeling this way!" But we were mostly shocked. I don't know why the possiblility hadn't occured to us, but it hadn't!
I hope you get the answer you want at your next appointment! Waiting is the worst!