Just because others are ordering old stuff doesn't mean you have to! For some, it is a question of completing their Cathe collection, for others it is a case of wanting more cardio options, and for others still, it is a case of having to go back to earlier choreography in order t olearn Cathe's style, so that they can come forward in time and conquer her newer style.
The Intensity series does not contain an extended cardio workout. It is primarily weights and circuit orientated, except for Imax 2 of course! I would say that if you are able to do Imax 2, in terms of choreography, you should have no trouble doing any of Cathe's cardio routines. So you can go forward or back in time!
As far as buying the Hardcore series is concerned, I think that since you can do the Intensities, the Hardcores are a reasonable goal for you. You have 2 options here. You can either buy the complete series now, because after pregnancy you will be able to use them, though not right away! Or, you can just buy now the ones you will be able to use and modify during pregnancy.
Whichever route you take, Imax 3 is super-tough and is not recommended for pregnant women. In general, interval workouts and pregnancy are not a good mix. There is the risk of a shortened oxygen supply to the foetus during the blasts. Also, as you get heavier, you simply can't get your heavier and less graceful self over the step. Issues of balance come in also during the second and third trimester.
Generally, I would say that you would be fine to order all the weight training workouts, and yo modify them as you get more advanced in your pregnancy. So, Muscle max, GS legs, and both upper body GS DVDs are a good purchase at this point. You could also get Stretch Max and Core Max if you wish or need to add that type of workout to your collection. But I am not sure for how long you could lie on your back doing core moves, nor how comfortable it would be to attempt ball work with a large belly.
High Step Challenge: is a bit like Bootcamp. It is a circuit workout that moves in cycles. A cardio section with the high step and floor, which is high impact, then complete body weight training, splitting the muscles worked into different cycles. It moves at a fast pace. Personally, during pregnancy, I'd pass on this one. You already have Bootcamp after all.
Low Max: even though it is low impact, do not be fooled. This is one tough, intense workout that really burns and shapes the lower body. It's fabulous, of course, and has received nothing but praise here on the forums. You could get this one to use in the first half of pregnancy and modify the blasts as you need to.
Hope this helps,
Clare