I've been getting mine coloured every 8 weeks since I got pregnant, no issues. My hairdresser gave birth in march and kept colouring her hair the whole time, so I figured I was in safe hands!

The biggest thing I think for some people is the fumes, so I generally ask for a seat close to the door, so I get more fresh air. If fumes etc bother you still, it's recommended you go on the quieter days/times at your hairdresser where possible.