Cervical length (CL) screening should be offered to singletons because there are interventions for those with a short CL. A transvaginal ultrasound (TVU) is the "gold standard" for CL. In singletons with prior spontaneous preterm birth, serial TVU CL screening is recommended between 16 and 23 6/7 weeks. Universal TVU CL screening between 18 and 24 weeks may be considered for low-risk singletons with the administration of vaginal progesterone for TVU CL≤20 mm; alternatively, transabdominal ultrasound CL screening may be considered with reflux to TVU CL screening for a transabdominal ultrasound CL<35 mm or inadequate visualization. CL screening is not recommended in multiples.