IUDs are normally put in position at the end of the woman’s menstrual cycle at approximately the 4th day of the woman’s cycle.
This is because there is a higher probability of the absence of pregnancy. Furthermore, the cervix is at this time easier to pass through.
In general, IUD implantation is painless (scoring 2/10 on a pain rating) especially for women who have given birth vaginally generally. Only the very smallest inserters are used (to facilitate easier progress through the cervix) for women who have not yet given birth or have given birth via caesarean section.
IUDs (or IUS; intrauterine system) that contain a progesterone reservoir are slightly larger and so less easy to insert. Nevertheless when put in place by experienced practitioners, these too do not cause, for the most part, any trouble or pain.