Laryngeal obstruction is a life-threatening condition which can sometimes be diagnosed by prenatal ultrasound examination. Dilatation of the fetal trachea is an important finding in these cases. Sonographic studies to evaluate the fetal upper airway were performed in 120 consecutive patients. The diameters of the trachea and pharynx were measured and our ability to visualize the trachea and the larynx was evaluated. The diameter of the trachea increased from a mean of 2.4 mm at 18 weeks to 4.6 mm at 38 weeks. The mean diameter of the pharynx increased from 4.4 mm at 18 weeks to 8.8 mm at 38 weeks. The fetal larynx was adequately visualized in 67%) of the cases, while the entire trachea was seen in 47% of the cases. Our success in visualizing the larynx and trachea was best between 20 and 30 weeks' gestation. This study shows that it is possible to obtain excellent views of the fetal airway in a high percentage of cases and reports the range of normal values for tracheal diameter. Early visualization of a diluted trachea may allow better management of a fetus with laryngeal obstruction.

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