How could a fibroid affect the pregnancy?

Yes: Depends on the size of fibroid.

Location and size: If the placenta implants over a fibroid it can impact fetal growth and increase the chances of placental separation later in pregnancy. Also if the fibroids are large they can degenerate during pregnancy causing pain, cramping and even preterm labor. Finally, if a fibroid is large and located in the lower uterine segment, it can obstruct fetal descent.