• Fetal Behavior;
  • Fetal Yawning;
  • Hypoxia



To study yawning activity in healthy fetuses and in fetuses at high risk.


Yawning activity was studied in 16 healthy and 22 high-risk fetuses. Studies were performed in the postprandial state at 09.00 and 12.00 in a quiet room with the woman in the lateral recumbent position. All ultrasound examinations were performed using a 3.5-MHz Acuson 128 PX curvilinear probe. Fetal lips, mouth, tongue, pharynx, larynx, trachea and esophagus were surveyed in serial coronal and sagittal planes. All fetal mouthing movements were analyzed by a review of the videotape in slow motion.


In both normal and high-risk fetuses, yawning was represented by isolated mouthing movements and consisted of slow opening of the mouth with simultaneous downward movements of the tongue. This phase occupied 50–75% of the yawning cycle. After reaching its maximum opening, the mouth remained wide open for 2–8 s and returned to its resting position within seconds. Growth-restricted fetuses demonstrated yawning patterns consisting of isolated yawns similar to those seen in healthy fetuses. Unusual bursts of fetal yawning activity were recorded in anemic fetuses.


Yawning activity in anemic fetuses may represent a compensatory process to increase venous return to the heart. Copyright © 1999 International Society of Ultrasound in Obstetrics and Gynecology