I have had two coils (Mirena) removed for TTC purposes.
On the first occasion with my Mirena I still had regular cycles and monthly periods and I conceived the first cycle after it was removed.
On my second Coil I had really irregular bleeding for 7 months but then for the next 3 months (prior to having it removed) I didn't have a period at all. I got my BFP within three weeks but unfortunately miscarried two weeks later.
I started a thread about miscarriage and coincidentally a lot of responses were off women who'd had early miscarriages after falling pregnant on their first cycle after Mirena removal.
When me and DH planned to TTC DC1 I was warned by my GP that miscarriages can happen on first cycles but I think that's more specific to women who don't have periods whilst the Mirena is in place.
The theory is that if you haven't been having periods then the endometrium layer in the womb isn't thick enough to accommodate a developing egg in the first few weeks and so a miscarriage can occur.
I don't know if there's any evidence base behind it. I do wonder though if that's why I had a successful pregnancy the first time round but miscarried the second time round. Me and DH plan on TTC again (the miscarriage only happened last week) but I'm going to wait a few months so I can have some normal periods first and let my endometrium layers get thicker.
I'm sure there are many, many women though who've had successful pregnancies after the first cycle of Mirena removal despite having not had periods, like I said, I don't know if the above theory is evidence based or something that has just been born of many women's experiences.
The best of luck in your TTC journey 