I kept my thrid pregnany a secret for three months. I'd had two miscarriages between #2 and #3 (and surgery for an ovarian cyst). We also wanted to keep it from family because two days after I found out I was pregnant we closed on our old farmhouse that had no heat, water, electric, etc. It had to be completely gutted, and we did 90% of the work ourselves. The whole time I was doing demolition I would say to my DH "Good thing no one knows I'm pregnant or they wouldn't let me do this stuff"
Well, after they found out they said I shouldn't be doing it, but by then the demo was done. During the rest of my pregnancy I did all the insulation, all the electrical, some painting, and some of the framing for new walls. The week before she was born I was on a stepladder installing the ceiling lights and fans. She was my biggest baby, too (9lbs,6oz) so I guess all that work didn't hurt her a bit!
Anyway, congratulations! Now ou have even more reason to knit!