In addition to longer periods at the beginning of use, a woman starting the IUD can expect some irregular bleeding for three to six months. A kallah who will definitely use an IUD from the start of her marriage should probably either have it inserted as early as possible, so that she can be well-adjusted to it prior to marriage, or find a different short-term contraceptive option for the very beginning of marriage. It is also worth noting that if the kallah is a virgin, insertion may be difficult.
We think it could be helpful for you to share the medical reasoning here with us, on the chance that there are other options that have not yet been fully explored.
Tizki lemitzvot!