At this point you can really do whatever, the more exercise the better
I wouldn't do crunches. But you can generally do anything you did prior to pregnancy unless you're having complications. I knew a girl who ran a mile every morning throughout her pregnancy. She's pg again and still running and going to the gym.
If you're worried you can do prenatal yoga or other exercises geared towards pregnant women or low impact workouts.
Keep up training back u will need it. No abdominal work. Squats n stuff r ok at a pool ect takes pressure from abdomine n back. Also if u have tight abs they'll most likely split which ul need to fix early so keep them checked. Mine were gone around 15w cause of how tight all those muscles were. But also pregnancy Pilates is extremely beneficial :)
Also some woman actually get told to cut down on walking like I'm not allowed cause my joints are really loose n it causes alot of pain in my legs hips n back. Not just the joints.