Like most aspects of pregnancy, what you can and should do physically is very individual. Cardio is no exception. But in an otherwise healthy pregnancy, you absolutely should keep up what forms of aerobic activity you can manage. The cardio exercise that works for me, could be totally different then for you. Or your comfort level throughout your various trimesters may change.
Generally speaking, in your first trimester there is not a great need to modify any of your aerobic regimen if you don’t want to. But….you may be feeling very ill. I know for myself personally, one of the first changes I felt physically was very early on in my first trimester, I struggled to run as that was the only time I would get very nauseous. So, for me, running wasn’t a great option the first couple of months. What did work for me was biking and rowing. Of course, if swimming is your exercise of choice, that is a save option as well.
As, I got closer to my second trimester, I was able to pick running up again for a bit. I even did a timed mile, albeit not very speedy. But that was about as far as I could go without starting to feel like I was putting extra pressure on my round ligament and pelvic floor.
Part way through the second trimester, I switched to stationary bike as my primary form of cardio. I would also still row often, but was cautious in my form. In particular, I wouldn’t extend as fully if I noticed that it was causing coning in my abdomen.
One thing I gave up for my full pregnancy was double unders. But honestly, I have never been good at them. So, I knew that they would both significantly spike my heart rate and they would probably tire out my pelvic floor easily since I was not good at them and had a tendency to hold my breath. I did still do single unders but would have to take more breaks then usual.
Speaking of heart rate, is that something that needs to be considered during pregnancy? Here you will probably hear a lot of different believes. Some say that you should not exert yourself so much that you could not still have a conversation. I personally would push myself beyond that point, but I also was used to pushing myself beyond that point pre-pregnancy. I wouldn’t push myself for so hard for so long though. And I made sure to be particularly careful when it was warmer, making sure that on those days that I felt a little weaker then normal or a little light-headed that I really hydrated and pulled back on my intensity. When you think about it, labor is a marathon, so why not train for it?