Is Cervical Dilation Common In Fitting Mirena Coil?

Hi I've had the mirena coil for the past 4 years and now started to bleed again, doc said it must be at the end of its life so removed it and tried twice unsuccessfully to insert a new one so has now referred me to hospital to get it fitted under a general anaesthetic as he says they need to dilate my cervix, is this a common problem for some people? I am 49, 10 stone, 5 foot 8 and have no medical problem apart from having really heavy periods that lasted for two weeks, stop for one then start again with backache and headaches until I had the mirena fitted which disolved all of those problems for me.