I'll be 18 weeks along tomorrow and I had asked my doctor about exercise at my last visit. She said that aerobic exercise is good as long as it's not too strenuous. She said to make sure that I listen to my body and only do what I feel comfortable with. With that in mind, I have been doing (until I get up the nerve to do more) fast paced walking for about 30 mins. But I plan on starting working out on a stationary bike and adding some light weights. I don't feel comfortable doing any sort of abdomenal exercises, so I avoid them.
I had lost 20 lbs before I found out I was pregnant. I remember working out pretty hard the day before I found out. I was hoping that I hadn't hurt the baby. But the baby and I are just fine.
Exercise is supposed to be very good for you and the baby! It also helps shorten the length of labor....And i'm all up for that!!!
Good luck!