Don't panic, this is standard practice for ultrasounds, and we happened to have an appointment today; this week counts 18 from the day the stork got its baby order confirmation email (or however these things work, I was never quite sure). After eighteen weeks of conjecture and hypothesis, hearing about scientific things like moon cycles, the effects of boxer shorts on sperm motility and conception genetics, the apparently conclusive correlation of morning sickness intensity to male gender likelihood, Science (capital 'S') has ascertained that our baby is... of the female variety. Which makes sense because her favorite place to hang out is in her placenta-pink womb-crib. And she's healthy and stuff! Which isn't surprising because she was doing a little boogie to the radio in the car and we all know that if you can get down and boogie then you're gonna be all right.
Also, it wouldn't be Science (with a capital 'S') if we didn't include an error-margin or probability analysis; they're about 80% sure about her bits being ladybits.
So you heard it here first - we're having a baby girl! (probably!).