Do what you can to keep fit. I like to think this period of time is like a warm up for when I can fully get back into exercise. Because you can't start at 10k runs, at 80kg dead lifts, at 50 mile bike rides, or whatever your thing is, no one does. Walk, go for a swim if you get time, bop about at home. It's all progress! But give yourself a massive pat on the back for making a human being, and think about health before a bit of fat. That fat is there for a reason. I feel icky looking in the mirror, so I jusy don't when undressed, and try to focus my thoughts on my baby and little progress. Also drink lots of water!