Mazal tov on your upcoming marriage!
In most cases, a woman’s hymen has already been somewhat stretched before her wedding due to exercise, tampon use, etc.
What remains is a small remnant of tissue around the perimeter of the vaginal opening, which may or may not be stretched or torn further when she first has intercourse.
Nevertheless, even if a woman doesn’t bleed, the couple are still required to separate due to dam betulim as a one-time decree following the first act of intercourse (learn more here).
Therefore, even if having an IUD inserted prior to your wedding may further stretch the hymen (although this is not necessarily the case), you would still need to observe the halachot of dam betulim, whether or not you see any bleeding.
Please feel free to get back to us with any further questions.
Bhatzlacha!