Take a look at this article Rachy - Seeing the Denist in Pregnancy.

Bleeding gums is definitely very common during PG. The 'normal' levels of plaque that are usually tolerated by your teeth/gums are no longer tolerated well during PG, hence the swelling/redness/bleeding. This is why it's really important to get a check-up and clean whilst PG (I know I did last time around and I will this time too!)