Most people will tell you that it doesn't cause any harm.

The truth is that very little study has been done on it.

It is thought to be harmless but that doesn't actually mean that it is.

After having had 3 m/c's I wasn't taking any chances & I went throughout my entire pregnancy without coloring my hair. It really didn't look that bad but I had heaps of greys showing by the end of it.

I persoanally would't take the risk with something that hasn't really been studied.