The risk of preterm birth in women with history of short cervix delivering at term in the previous pregnancy: a retrospective cohort study

Purpose To investigate whether women with a short cervical length (CL), but delivered at term in the first pregnancy might have increased risks of having short cervix and spontaneous preterm birth (sPTB) in the subsequent pregnancies. Methods This is a retrospective cohort study including singleton gestations who were delivered between Jan 2011 and Dec 2018, who had had one childbirth experience and who had transvaginal sonographic CL assessment performed at mid-trimester (18 ~ 30 weeks) in both pregnancy. The women were divided into four group according to the history of preterm birth and a short cervix (