Preterm birth is a major public health problem in terms of perinatal mortality, long-term morbidity and health economics. It is responsible for more than half of all neonatal deaths. In a UK multicentre study of survivors born before 26 weeks’ gestation, 80% were disabled at the age of 6 years. The economic burden of prematurity relates not only to the initial neonatal intensive care but also to the longer-term increased use of medical, social and specialist educational services, as well as the lost economic productivity. A series of studies have demonstrated that administration of progestogens to women with a singleton pregnancy with a short cervix approximately halves the rate of spontaneous preterm birth. The availability of an effective intervention now provides a rationale for population-based screening for preterm birth. The most widely adopted approach to identifying pregnancies at high-risk of spontaneous preterm birth is based on a previous history of preterm birth. Evidence suggests that more effective screening can be provided by the sonographic measurement of cervical length at mid-gestation. However, there is currently no clearly accepted method for population-based screening. The rates of extreme (<28 weeks), early (28-30 weeks), moderate (31-33 weeks) and mild (34-36 weeks) spontaneous preterm birth were 0.2%, 0.2%, 0.6% and 3%, respectively. The best prediction of spontaneous preterm birth has been shown to be provided by cervical length (area under the receiver–operating characteristics curve (AUC), extreme 0.903, early 0.816, moderate 0.784 and mild 0.617) and this is improved by adding obstetric history (AUC, extreme 0.919, early 0.836, moderate 0.819 and mild 0.650). For a 10% screen-positive rate, models using cervical length and obstetric history have a sensitivity of 81%, 59%, 53% and 29% for extreme, early, moderate and mild spontaneous preterm birth, respectively. In conclusion, a model combining cervical length and obstetric history provides a better prediction of spontaneous preterm birth and the sensitivity of screening improves for increasing degrees of prematurity.