I lost weight from pre pregnancy to post, but not by trying. Don't try to lose weight (stay away from diet stuff with artificial sugar), don't focus on your weight at all.

Do focus on the fact that you are the only source of nutrients and vitamins for your baby, so consider yourself a vessel for getting the proper nutrients to your bub and avoid crap. A mother's diet can contribute to obesity in newborns and gestational diabetes is a concern.

I really really enjoyed tuna, baby spinach, chick pea, avocado and baby beetroot salads during my first pregnancy. My second pregnancy I had bad morning sickness and acid reflux and ate a lot of unsalted, raw nuts. So not low in fat but healthy food will see you happily through your pregnancy without excessive weight gain (but you should expect to put on 11-14kgs by full term, that's just inevitable).