Way back when my wife was pregnant with my son, we didn't mess with that ultrasound sissy stuff. We just sat her down on top of a stereo speaker, played some "Love to Love Ya, Baby" by Donna Summer (the long version with lots of moaning) and watched for the erection. The boy did me proud. Sometimes the old ways are the best ways.
Anyway, congratulations. I hope you have as much fun as I have had.