Can your commander stop you from using the chapter 8 pregnancy to separate?

I suggest you read AR 635-200, Chapter 8. You may also read 1-19 in the same regulation.

Have you read that regulation?

What do you mean "stop" them? The commander is supposed to counsel a pregnant soldier on all her options once medically determined to be pregnant. If the soldier elects to be chaptered out, then it goes from there. Do you mean can a commander try to coerce a soldier to not get out on a Ch 8?

If you go read the chapter it says "conditions affecting separation for pregnancy."

It's a weird and vague question...