Whether IUD insertion itself renders a woman niddah is subject to halachic debate. Our site’s position is that the standard procedure, which is carried out with a very narrow instrument, does not render a woman niddah.
Bleeding immediately following IUD insertion is considered blood from a wound (dam makkah) and does not render a woman niddah. With any IUD, the insertion procedure is likely to cause trauma to the cervix. The Gynefix is embedded in the uterine wall, so its insertion can also cause uterine bleeding due to trauma.
We follow the position that bleeding that continues for longer than a day or two, or that begins more than a day after the procedure, cannot automatically be considered dam makkah. The concern is that uterine bleeding not directly attributable to Gynefix insertion may have another source. This concern is stronger at a time of month when a woman expects to menstruate (her veset days).
After IUD insertion, the leniencies of stains do apply. So we recommend reviewing the laws of stains (as by reading our site’s articles on “Stains” and “Toilet Paper“) beforehand. Within a day or two of Gynefix insertion, you may treat bleeding as insertion bleeding (dam makkah) that does not make you niddah. Afterwards, careful observance of the laws of stains should help head off any further questions.
Please write back with any follow up questions.