Tweetable abstract
Cervical length(CL) measured by transvaginal ultrasound(TVU) has good performance to predict spontaneous preterm birth(sPTB) <28 weeks and it should be recommended as a mid-trimester screening test. The number needed to screen to predict one sPTB <34 weeks in women with CL ≤25mm is 121 and 248 screening tests are necessary to prevent one sPTB <34 weeks using vaginal progesterone prophylaxis. We suggest that women with CL≤ 25mm are at risk of sPTB <34 weeks and should receive treatment to prevent sPTB, but also those with CL between 25-30mm are at risk for late sPTB and should receive optimum antenatal care.