Preterm birth

The risk of spontaneous preterm birth (sPTB) is increased in women with a history of previous sPTB and the risk is related to the gestational age at which the PTB occurred. Additionally, the risk of PTB is inversely related to cervical length at 20-24 weeks of gestation in the current pregnancy.

A model combining cervical length and obstetric history provides a better prediction of spontaneous preterm birth than either factor alone and the sensitivity of screening improves for increasing degrees of prematurity.

• For a screen positive rate of 10%, the detection rate is about 80% for birth at <28 weeks of gestation, 60% for birth at 28-30 weeks and 50% for birth at 31-33 weeks.

When you obtain the FMF Certificate of competence in cervical assessment you will have access to this calculator which will allow you to assess the risk of sPTB.

1. Beta J, Akolekar R, Ventura W, Syngelaki A, Nicolaides KH. Prediction of spontaneous preterm delivery from maternal factors, obstetric history and placental perfusion and function at 11-13 weeks. Prenat Diagn 2011;31:75-83.
2. Celik E, To M, Gajewska K, Smith GC, Nicolaides KH; Fetal Medicine Foundation Second Trimester Screening Group. Cervical length and obstetric history predict spontaneous preterm birth: development and validation of a model to provide individualized risk assessment. Ultrasound Obstet Gynecol 2008;31:549-54.