Yes! You CAN do this. With my second pregnancy, I was feeling like if I didnt increase my strength and endurance, I was going to be exhausted trying to lift two children, and all of the baby gear, etc. At the time, I was in the first trimester and very tired. And I could hardly carry around my first child (at that time, my first child was only 9 months old) At the time I was very surprised to be pregnant again, and I hadnt lost the baby weight from the first baby. I had just stopped nursing. I was just overwhelmed.
I joined a mommy & me fitness group which was great. I went 3 days a week. I gained muscle tone in my arms and back. I didnt do ANY ab works (no sit ups, no push ups). I jogged a tiny bit, but mostly walked fast while pushing my first child in the stroller. I did squats and some other leg lifts, etc.
It not only helped me to not gain too much weight. But once the baby was out, I was healthy, and able to manage two babies. Now my children are 9 months and 25 months. And best of all, I weigh 132 pounds, and I have lots of muscle tone and I am able to manage two children with lots of energy. Keep moving. Ask your OB what you can do. It will make such a difference!