I had a 3cm fibroid found at either my 6 week or 12 week scan.
It was in the uterus wall, right near the opening of my cervix, on the right hand side.

my OB was not at all worried about it, and told me that it would probably move up and out of the way.

At my 20 week scan it was 6cm, and my OB booked me in for a scan at 36 weeks just to check. At that scan they could not see anything at all, there was no sign of it.

The only complications I was aware of were that it could implode (can be quite painful but not harmful to the baby) and it can grow or shrink due to hormones.

I had a vaginal birth. At no stage did my OB talk about anything different.