Preterm birth (PTB) is a major cause of perinatal morbidity and mortality. Worldwide, about 15 million babies are born too soon every year, causing 1.1 million deaths, as well as short- and long-term disability in countless survivors. Few prognostic tests are available to predict PTB. A short transvaginal ultrasound cervical length (TVU CL) has been shown to be a good predictor of PTB.Different strategies have been adopted for prevention of PTB. The evidence supports the use of vaginal progesterone in singleton pregnancies with short cervix, while cervical cerclage seems to be beneficial only in the subgroup of singleton gestations with both prior spontaneous PTB and TVU CL ≤25mm, and not in singletons without prior PTB, nor in multiple gestations.