Prediction of Preterm Delivery with Serial Cervical Length Measurements After Threatened Preterm Labor

Inclusion Criteria: * Singleton pregnancy at 23+0 - 33+6 weeks' gestation * Age \> 18 years old * Patients should be capable of providing consent to participate in the study Exclusion Criteria: * Previous spontaneous preterm (20+0 - 36+6 weeks' gestation) delivery (including history of pregnancy loss due to cervical incompetence, i.e painless cervical dilatation prior to 24 weeks' gestation) * Treatment with 17 hydroxyprogesterone caproate due to a previous spontaneous preterm delivery * Detection of a cervical length \< 25 mm during routine ultrasound \< 24 weeks' gestation in asymptomatic patients (i.e patients that do not complain of uterine contractions or patients with no uterine contractions documented on tocometry) * Treatment with vaginal progesterone or micronized progesterone due to a cervical length \< 25 mm * Cerclace placement in the current or in a previous pregnancy * Multiple pregnancy * Age \< 18 years old * Preterm premature rupture of membranes (pPROM) upon initial presentation * Müllerian malformations * Prior cervical surgery