With our second, who was unexpected (though not unwelcomed!), I walked into the ultrasound room and said, "Can I have a bucket next to the exam bed? If you find twins in here I am going to throw up. I DO NOT WANT TWINS." It turned out that both the male ultrasound tech and the female "chaperone" who somehow needed to be in there were BOTH parents of twins. ;) Open foot, insert mouth.
But seriously. Put me in the JustKate camp of "fall over, hit my head, and die." No way. Even if I suspected twins, I would be ignoring that suspicion. I don't need any more anxiety right now!!