Hello Robslea,
In my view, a student who is pregnant needs teaching for two - one that concerns itself with the safety and effect for the mother and one that concerns itself with the safety and effective of the developing fetus.
For this reason it would be my preference to have students that are pregnant study with a teacher who has substantial pre-natal yoga training. The needs of the two aforementioned students grow over term and so not only does the teacher need to be able to serve both students now but also in the second and third trimesters.
What I do with such students when they come to general classes is explain to them what the yoga viewpoint is, as I’ve studied, learned, and practiced it. I can modify some parts of the general practice for them but they would be best served in a pre-natal class. If they choose to stay they should be aware that it does take require a great deal of the teacher during class.