I'm 15 wks and last night my fiancé and I spent sometime at the hot springs. I'd done some research & was conscious of the fact that extreme heat can be bad for the baby so we decided to just lay in the foot spring which was only 34-36 degrees, so no hotter than a warm bath.
However afterwards when I went to the toilet I noticed some pink spotting so I put panty liner on to monitor it & two hours later it had turned to light brown spotting. 
It has stopped this morning but I'm still curious as to see if anyone else had experienced this? 
                
                             
        
Re: Spotting after bathing in hot spring
Sex?
Its rare that heat equivalent to a warm bath would cause issues with your pregnancy.
LFAF Summer 2016 Awards:
The brown spotting continued the next day so I went and had things checked out and an ultrasound showed our baby girl actively moving with a healthy heart beat. I'm still spotting today (brown only) so I guess I'll just monitor it. No need to panic now. First time pregnancy is a learning curve.
Light spotting can also be totally normal which I know seems pretty scary when it's happening to you!