
and welcome to our board!
My name is Mandy, the other host of this board. I'm so glad you've joined us.
I don't know anything about IUD, I've never had one. But in the beginning of our TTC journey I did read a few articles on the "Shettles Method" of gender selection. It is based on the theory that "girl sperm" travel more slowly than "boy sperm" but live longer. Therefore if you want a girl it would suggest that you stop BD about 3 days before you O. That way by the time you O the boy sperm have "died" and the slower girl sperm, who are still alive, have finally made it to the egg.
To me, since you have 4 boys (doesn't seem like getting pregnant is an issue for you, is it?) it would be worth trying for a cycle or two.
I don't know how effective or even IF it's effective but it's worth researching.