Weight loss before baby!!

I'm kicking myself now because I am (my husband an I) wanting to stop my birthcontrol shortly, probably in the next couple months. I am kicking myself because I should have been getting healthy a long time ago. I weigh 166 lbs and my height is 5'1. I would like to loose around 25-30 lbs. can I still try to loose weight if I get pregnant? What are the "rules" on this. Thanks!!!!