Hi, congratulations on your pregnancy.
Try not to worry too much, I know its hard, but I was diagnosed with fibroids and I've gone on to have 3 healthy children !
Funnily enough, when I had my first meeting with the MW with baby 3, she questioned my dates as she said I was further gone than my dates suggested. Maybe that was my fibroid ? I dont know ?
Anyway, the fibroids do stretch and grow as you grow, but they shouldnt have any bearing on the growth of the baby, unless they are quite low down which would affect the baby when he eventually comes out.
Mine was quite low down, so I had to have a couple of extra scans at 30 and 35 weeks or so. In my case, as my uterus stretched, my fibroid stretched upwards too, and I had a normal delivery.
I could feel a hard lump, and apparantly it was the size of an orange.
Nobody was particularly concerned, and they shrunk after the birth.
One thing you might find after the birth is that you might bleed for longer than you expected. On the other hand you might not.
Hope all goes well