As long as your are drinking lots of water before and after your baths you should be ok, I think the reason your not supposed to is that your body temperature is already elevated from being pregnant and the babies body temp is high inside of you as well, so you don't want to overheat. However, our bodies are very good at telling us when too much is too much, if you experience being dizzy, light headed, or increased heart rate during or after your bath it might be too hot.