I'm not really sure what you are asking, but i'll try to answer it from what I think you are asking. If you have a guy who is .....lets say 200 pounds, and he has 30 pounds of fat on him, it looks like this:
30 pounds of fat
200 pounds of wt. X 100 = 15% bodyfat
Now, if he wanted to get a bodyfat reading of 10%, he could either diet down or gain 100 pounds of muscle (with no fat gain). It would look like this:
30 pounds of fat
300 pounds of weight X 100 = 10% bodyfat
Alright, I now this is impossible, and you all are probably laughing your asses off, but I did it! LOL, JOKE, I am just trying to make a point here.
Now, as you can see, although no fat was lost, because you gained muscle mass and increased your total bodyweight, your percentages got lower. This does not necessarily mean you are leaner. My advice, AFTER YOU PREGNANCY, is to decide whether or not you want to lean-up, or add muscle. Don't try and do both at the same time. I'm gonna stop here just in case I totally missed your question and am typing irrelevant crap.
MR. BMJ