GROUP B STREP

Ok so i hardly ever get a reply on here for some reason but im hoping someone can help. if you have pre term labour caused by GBS what type of labour is it? (eg. contractions/prom/dilating) the only reason i ask is i previously gave birth very premature and was dilated to 5cm with no pain, the hospital said i have cervical incompetence. but i also tested positive for GBS but they said this wouldnt of been the cause? does anyone have any idea as google not giving me any informatiin? thanks