should i let my bitch atend an agility session. when she may be 3 weeks pregnant. it has not been confirm yet.

I wouldn't personally - I did let my bitch go to an obedience weekend when 3 weeks pregnant (last litter 2 years ago) but she had had an infection so I didn't think she would be, and it was just heelwork and recalls, not vigorous exercise with jumps and A frames. At 3 weeks the foetuses are starting to attach to the uterine horns, and any accidental knocks or getting overheated could have very serious effects. I was strongly advised on this board not to even let her go to training classes this time round.

I wouldn't to be honest.  Whilst keeping a bitch fit during pregnancy is vital, agility is a bit more taxing on the joints & everything else.  I always err on the side of caution with my girls, I don't attend dog shows with them either as the risk of picking up some nasty bug (such as kennel cough) is likely.