Permanent hair straightening?

Does anyone get their hair permanently straightened regularly?  I?ve been doing it about 9 years I guess and it?s always been the CHI straightening that grows out, as opposed to the other treatments that fade out.

So, first question, is the CHI or any permanent straightening safe to do at all?  I know you can dye your hair in the 2^nd trimester but I?m reading conflicting things on straightening.  The American pregnancy site, or whatever that .org site is, says permanent straightening is okay.  When I first started getting it done the stuff they used was pretty strong smelling, but I don?t notice the smell anymore.  Don?t know if the formula changed or I just got used to it.  But some other people are saying they wouldn?t do it at all.  I need to ask my OB but I don?t even know if he would know the process I?m talking about.  Would I just need to tell him what chemicals are in it?

Second, I?m also reading that our hair changes and that it might not even take to the straightening like it did previously because of all the hormone changes.  Anyone had any experience with that? 

I?ll ask my stylist in a few weeks once we announce to everyone (my mom uses the same stylist and I don?t want her to tell my mom accidentally), but I?m just trying to find some info.  I?m kind of mad at myself because it?s been almost 10 months since I?ve had it done and it?s starting to look rough because it?s getting warmer/more humid here.  I was really hoping to get it redone during the 2^nd trimester so that I didn?t have to deal with it during the crazy humid and hot spring and summer months here.