Created an account just to share my experience on this thread for reference for others.
I’m currently 30 weeks. Throughout pregnancy I’ve done 8-14 hour weeks. I was a well-trained amateur cyclist beforehand. I have had relatively minor symptoms so that’s helped me to feel good on the bike. I mostly mountain bike and do gravel biking or paved rail trail riding otherwise for the most part. I have done a lot of mountain biking while pregnant. More rides than I would have done while not pregnant! Typically about 3-4 mtb rides outdoors per week, sometimes more, not usually less, plus a couple of non-mtb rides, usually riding 6-7 days a week. I also do lots of hiking to mix things up (not something I liked to do prior to pregnancy). I have lately had to start taking a recovery day each week, sometimes two, when normally I would have just done a recovery ride (that no longer cuts it).
I was able to do just about anything I wanted during the first 16 weeks or so except put my heart rate in the highest zone. My HR max prior to pregnancy was about 195. During pregnancy I very rarely got it up above 180ish. It just didn’t want to go that high and immediately after becoming pregnant it was apparent that everything was more difficult. I did some interval workouts and some hard rides during this period but mostly did easy (zn 1-2, sometimes zn 3 out of 7 zns) rides. I didn’t worry to much about how hard or fast I was going on non-interval days - I just rode at whatever pace was comfortable.
From 16 weeks through now (30), I have been able to continue to do mostly what I want but have definitely been quite a bit slower. Still mostly doing a lot of z1-2 rides but recently got a smart trainer and have loved doing some interval workouts on that. I haven’t done any anaerobic work. Could probably do some zn 5/7 intervals. Mostly feel comfortable in zn 4 and do some sweetspot rides. I need more recovery after sweetspot rides that normal.
Based on how I feel right now, I think I’ll be able to continue doing mostly zn 1-2 rides with 1-3 interval sessions sprinkled in throughout the week with reduced volume until close to the end. I think I will have to regularly have 1-2 recovery days per week but will add more if I start feeling cranky.
I actually had never done an FTP test before and still haven’t done one now. My garmin had set mine at 3.3 w/kg (since the very beginning of my use of it so it definitely wasn’t accurate) and I just started doing a few trainer rides at that FTP. I’m positive my non-pregnancy FTP is much higher. But that has felt like a good FTP to ride with. I may decrease it some as the pregnancy progresses since everything just keeps getting harder.