Is group b strep a reason for going into labour early?

Yes: Group B strep can induce early labor.

Preterm labor: Yes, Group B strep infection could cause pre term labor

GBS early labor?: Group B strep colonization occurs in many pregnant woman ( one study estimates10%). Some studies reported that GBS is associated with premature labor and may have effect on member rupture. However other surveys of large groups of women could not repeat these finding. Talk to your doctor with him/her about risk, your particular situation and come up with a plan together with him/her