Hi, S.! I'm not familiar with any downtown prenatal yoga classes other than the ones Northwestern Memorial Hospital offered (2 years ago now for me). There were two different instructors at the time and I really loved Mona. The other instructor seemed to forget we were pregnant and focused on more intense and fast moves rather than moves to help alleviate pregnancy pains, promoting relaxation, and tips to use for future labor and delivery. I could see how the latter teacher's style in general would have turned off anyone from yoga if they were just starting with that prenatal class.
That said, I have found prenatal yoga very beneficial for me in both my pregnancies. With my second pregnancy, I found a yoga practice (southside - Beverly Yoga Center) that was more what I was looking for and needed: strengthening, keeping me somewhat fit, alleviating certain pains that come up, practicing breathing techniques that really helped me during labor and delivery, knowing and practicing poses that would assist me in labor, learning to focus in the midst of pain, etc. My first delivery ended up in cesarean after 22 hours of unmedicated labor and 11 months later I delivered VBAC unmedicated which I attribute to many factors including having a good prenatal yoga practice. I even delivered the second time in some yoga poses. So even if you're planning an epidural having some relaxation techniques for that start of labor can still be helpful to manage the initial pain.
Good luck finding a good class....