(Abstracted from JAMA 2017;318(23):2317–2324)Spontaneous preterm birth is a major cause of maternal and neonatal morbidity; it is estimated that preterm birth caused 1.1 million infant deaths in 2015, as well as short- and long-term disability in survivors. Cervical pessary is a silicone device used to prevent preterm birth, although its efficacy is unclear as there have been contradictory results in randomized controlled trials (RCTs) in women with singleton pregnancies and short cervical length.