hot baths

So, I am a huge fan of hot baths, expecially at the end of a long work day. I am currently 19 weeks and I take a bath almost every night. I did some research and most sources say don't let your body get over 102 degrees, but I have never taken my temperature while in the bath. How do I know if the water is too hot?  And should I be concerned?  I read that most people get out of the bath before they get too hot just due to the discomfort??  Any input?

My doc said as long as you fill the tub and don't keep adding new water it was ok because the water naturally cools down so you are not in "hot" water too long.  Just don't add new hot water to keep the temp up.  But if it starts out really hot I would try to cool it down.  Why do something that could be dangerous.