That is a good question. As far as I can tell,( according to the article below) the reason Mirena is recommended for women who have already given birth is the size of the IUD as compared to the size of the cervix can make insertion difficult. My friend I'd on her second Mirena and doesn't seem to have had any issues with it, but she's never had kids.
I've never even had sex, but they put mine in during my surgery, so I didn't feel a thing. ;)

https://www.aafp.org/afp/2018/0901/p304.html

https://www.mirena-us.com - this website has information on kyleena, skyla and Mirena. Mirena does have a higher dose of hormones compared to the other two.

Haha, yeah, I'm very glad! Also didn't hurt that I was on strong pain killers until I left the hospital the next morning, lol.

This is great news to know! And very nice that you were asleep when yours was inserted! Yay for that!

I am getting the Kyleena in after I have an ultrasound in mid to late May. I am on a progesterone only pill right now because I get migraines with auras. My OBGYN said a lot of her patients have much success on the kyleena, and she mentioned that Mirena is better for people who have had children (I have also heard this from my friends but I’m not sure why). I believe kyleena has the lowest amount of hormones for an IUD. I try to trust my doc and my body and not freak out too much bc I know everyone’s body is different. I will be closely listening to mine after I get it!

I had a Mirena IUD put in after/ during surgery 7 weeks ago, so I'm new to it, but so far I like it. My bleeding is much lighter and so far I've not noticed any side effects, unlike when I was on hormonal birth control and when I tried the mini pill ( progesterone only).