Ultrasound evaluation of the normal fetal upper airway and esophagus.

Because congenital anomalies of the fetal neck may alter the normal anatomy of the upper airway, a prospective evaluation of the fetal trachea, hypopharynx, and esophagus was undertaken in 50 consecutive fetuses of 18 to 38 menstrual weeks. The cervical trachea was visualized in 47 of 50 fetuses (94 per cent) and had an average internal diameter of 2.6 mm with a range of 2 to 4 mm. The average diameter of the hypopharynx was 5.5 mm on parasagittal section (range 4-8 mm) and 7.1 mm when imaged in the coronal plane (range 4-10 mm). The configuration of the fetal hypopharynx and larynx varied with fetal respiration and swallowing in a characteristic manner. In no case was a persistent fluid collection observed in the region of the cervical esophagus, suggesting that the fetal esophagus is collapsed in the resting state.