HopingCat, beware long post....
Basic rules for exercising when pregnant:
Make sure your midwife knows what exercise you're doing once you're up the duff - there are some things that will mean exercise is a no-no e.g. if you find out you're having triplets
Don't start anything new i.e. don't start training for a triathlon...
Try not to get too hot.
Drink plenty of water.
Being out of breath is fine, as most people get puffed quite quickly when pregnant. If you think of sitting on the sofa eating pie as effort level 1 on a scale of 1-10, and 10 sprinting for a bus, try to keep your effort level around 5-7. This should be a good sustainable level where you know you're working but you can still talk!
No lying on your back from 2nd trimester onwards (puts pressure on the vena cava, can make you feel dizzy).
Be careful holding weights above your head (e.g. shoulder presses) as it can make you feel dizzy. You can get round this by doing other upper body work, or try doing your shoulder presses with one arm at a time while sitting on a swiss ball (best) or on a bench/chair.
Re abs, you should check if your tummy muscles have come back together (ignore if you've done this!). Some separation is totally normal, otherwise there wouldn't be room for the baby. Unless you have a hernia it's not really like a big 'ole in your tummy muscles, more like a thinning of the tissue that joins the 2 sides of the muscles that make up the classic 6-pack. Easy to do the check: lie on your back, knees bent as if you were going to do some crunches. Put your fingers just above your belly button (the place where max separation occurs) and you should feel a gap/softer section. Lift your head neck and shoulders up off the floor. Separation of a couple of fingerwidths is normal. Anything more, you need to do some special rehab work (v. easy) and avoid some specific exercises. Otherwise continue with Davina abs until you know you're pregnant. Let me know.
There are plenty of abs exercises you can do when pregnant (contrary to popular belief), but I would advise you not to do the abs section in the Davina DVD. Happy to give specific exercises!
Lifting weights while pregnant is fine, but you want to switch to lighter weights, poss increase the reps and ensure really good posture to protect your back. Always bend ze knees when picking up weights, even if you think they're super-light.
When ttc, there is nothing that you can't do - but to give yourself best chance I wouldn't embark on a hairy scary training regime or a crash diet, it'll just divert your body's energies from TTC.
Plenty of people continue to play netball for a bit while pregnant, but it's not really advisable, mainly because you don't want anyone elbowing your bump and don't want to be hit in the tummy. Badminton is fine, but you should bear in mind that you may find your balance goes a little and you will sometimes find it awkward to stretch to come in over the top of a shot.
Most importantly (and it sounds a bit airy fairy) listen to the way you feel. If something just feels 'wrong' or awkward, or uncomfortable then don't do it. If you feel sick, faint, dizzy etc - stop.
Always happy to wax lyrical on this topic, am a personal trainer specialising in pre and post natal, work closely with midwives and HVs to try and encourage activity in pregnancy and have a total bugbear about the fact there is so much bad advice out there - and always fuddy duddy old GPs who say you should do no more than lie on the sofa getting fat and depressed.