32 weeks scan shows that my placenta is touching my cervix?

I had a scan at 20 weeks and it showed that my placenta was low but not covering OS, i have had my 32 weeks scan to check the progress and the sonographer said that it is now touching my cervix and completely covering my OS. i have another scan in next weeks and a appointment with the consultant, does anybody know what the chances of it moving will be and if it doesn't what week will they do a c-section?