I did yoga til I was 8 1/2 months pregnant (got too disproportionate!) and I never did a specific prenatal one. I just followed the pregnant lady on the video instead of the non-pregnant people. :) The videos usually have a beginner, an intermediate, an advanced, a pregnant person, someone with knee problems, etc, so you can watch a specific person.
The only moves we couldn't do was the one where you lay on your belly on the ground (snake something?). Instead you do cat curls. And when you do intense stretching on the floor with your legs, you use the bands so you don't overstretch (because we have the hormone elasticin already doing that for us). You can't do anything on your back either- when they get to that at the end, the pregnant lady just laid on her side until the video was over.
Other than that, you can do chair and downward dog and everything else! Downward dog went a long way to helping me not have ANY back pain this pregnancy! Amazing! So I would suggest just getting a yoga video from the rental store! There are tons. They should have prenatal yoga ones too!