"Generally," she agreed, "but this isn't a typical situation, and I'm afraid all of my confidence has gone and left me, never to be seen again." She was being dramatic, of course, but she was nearly frozen with fright at the prospect of being a mum, and this was the best she could do. Be dramatic.
The feel of wand against her belly made her supremely nervous, but that wasn't atypical for the evening, so she remained still. "How far along would I need to be to see?" she said. "How far along do you think I am?"
Once the blue sparks showed, Tonks stared at them for several seconds, speechless. When she did find her words again, they were high-pitched and squeaky. "Blue means boy? I'm having a--son?"