A newborn is found to have stridor. What is the the commonest cause of stridor in a newborn?

Laryngomalacia is the most common cause of stridor in infants, and is also the most common congenital laryngeal abnormality, accounting for approximately 60% of cases. Stridor occurs as a result of prolapse of the supraglottic structures into the laryngeal inlet on inspiration. Also know: Stridor is generally of laryngeal or tracheal origin. As a general rule, inspiratory stridor originates from the supraglottis and glottis, expiratory stridor from the trachea, and biphasic stridor from the subglottis. Ref: Yates P.D. (2012). Chapter 33. Stridor in Children. In A.K. Lalwani (Ed), CURRENT Diagnosis & Treatment in Otolaryngology--Head & Neck Surgery, 3e.