RESUMO
OBJECTIVE: To investigate the mechanics of fetal swallowing using color Doppler technology. METHODS: The fetal face and a profile were imaged sagitally in ten fetuses at 36-41 weeks' gestation. Color-flow Doppler signals were superimposed on each gray-scale image to assess the direction and location of amniotic fluid (AF) flow with respect to anatomic structures of the fetal upper gastrointestinal and respiratory tracts during the act of swallowing. Further analysis of fetal swallowing movements was performed by a review of the ultrasonography videotapes at a slow speed. RESULTS: An initial stage of fetal swallowing was characterized by two to six sucking movements and the introduction of an AF bolus into the oral cavity. The soft palate superiorly and the tongue posteriorly and inferiorly obstructed the further flow of AF. The final stage of swallowing was characterized by low-frequency tongue movements, upward laryngeal and epiglottic movements, and narrowing of the lumen of the pharynx, directing the fluid bolus caudally. However, some AF was directed into the nasopharynx as well as the trachea. CONCLUSION: The swallowing pattern in the term fetus differs from that in the infant and adult, in that the oral and pharyngeal phases appear to be less completely developed.