If you have been "fit and muscular"... do not make the mistake of "hybernating" throughout the pregnancy. You can still do most of the exercises that you have been doing before pregnant. Brisk walking is especially good - it helps with bowel movement, too! Others like yoga and even light aerobics and running could be continued - they key word being do what you HAVE BEEN DOING, what your body feels comfortable with. If in doubt, check with doctor. You need strength and muscle during delivery as well - and it would be much harder to regain your weight and shape if you choose to "hybernate" during pregnancy. Also, exercise some self control - avoid high sugar and high calory stuff - in contrary to popular belief, you do not need to "eat for two"... you only need 20% to 30% extra. Which is overall one extra bowl of rice or 2 cups of milk! 2 cents worth from a mother of three that is pretty much the same size before and three-after!