I think what you're referring to is the fact that heat can kill off sperm. Some people say hot baths etc can lower a man's sperm count because the heat will damage the sensitive sperm. cooler environments are more ideal for sperm...apparently this is why the man's junk "hangs low" lol, it's further away from the natural body heat.
hot baths for women...well i don't think it is an issue for women TTC...really it's just for the man and his sperm. But i think if he is healthy and has a good sperm count to begin with, it shouldn't be a problem.