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fetal yawn

mise à jour du
30 décembre 2001
Obstet Gynecol
Fetal Yawning activity in normal and high-risk fetuses:
a preliminary observation
 B. Petrikovsky, G. Kaplan and N. Holsten
NYU School of Medicine, Manhasset, New York, USA
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The description of fetal yawning activity has been limited to case reports. Sherer and associates' described yawning movements in a 20-week fetus. Sepulveda and Mangiamarchi reported repetitive yawning movements in a 27-week fetus over a 7-min observation period. In both cases, yawning activity was detected incidentally. We report our observations of yawning activity in 38 fetuses between 36 and 40 weeks of pregnancy, performed as a part of a fetal behavior study protocol.
fetal yawn
Of the 38 fetuses studied, 16 were appropriately grown and were products of healthy pregnancies (Group 1). The remaining 22 fetuses were products of high-risk pregnancies: nine of Rh-immunized mothers and 13 growth-restricted fetuses (Group 2). Fetal growth restriction was diagnosed when estimated fetal weight was :9 10% below the norm for gestational age. Gestational age was established in the first trimester on the basis of crown-rump length (CRL) measurements. All rnothers were referred for fetal assessment, including a biophysical profile, for the following indications: decreased fetal movernents, previous stillbirth, suspected postmaturity, fetal growth abnormalities and Rhimmunization. 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 XP curvilinear probe. Fetal lips, mouth, tongue, pharynx, larynx, tracheal 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. Yawning was definedas a prolonged wide opening of the mouth followed by a quicker closure of the mouth. All neonates in both normal and high-risk pregnancy groups were born in satisfactory condition. The 1- and 5-min Apgar scores were greater than 7 and 9, respectively, in all cases. Rh-iminunized fetuses had significant anemia (hematocrit between 17 and 28) and required in utero blood transfusions. The diagnosis of restricted fetal growth was confirmed postnatally. Cord blood pH was analyzed in all fetuses in Group 2. A paired t test was utilized for statistical comparison of groups.
Yawning activity was detected in 18 of 22 fetuses in Group 1 during 60 min of observation. The fetal face in either coronal or sagittal view was visualized during 75-90% of the observation time. In most cases, a fetal yawn was an isolated event and consisted of a slow opening of the mouth with simultaneous downward movement of the tongue. This phase occupied 50-75% of the yawning cycle (between 9 and 13 s). After reaching its maximum opening, the mouth remained wide open for 2-8 s (20-45% of the yawning cycle) and immediately returned to its initial position (5-10% of the yawning cycle or 1-2 s). Growth-restricted fetuses demonstrated yawning patterns consisting of isolated yawns, similar to those seen in healthy fetuses.The number of yawning movements over a 60mn observation period was 5±4 in normal fetuses, 8±5 in growth-restricted fetuses and 12±6 in anemic fetuses. Unusual bursts of fetal yawning activity were recorded in anemic fetuses. These bursts were characterized by clusters of three or more yawns, with the temporal characterisfics of isolated yawns described above.
In neonates and adults, a yawn consists of an involuntary wide opening of the mouth, with maximal widening of the angle of the jaw, long and deep air inhalation through the mouth and nose and a slow expiration. This is a brainstem-mediated reflex that serves to reverse relative hypoxia. Drowsiness and attendant decreased mentalactivity, which are associated with this borderline hypoxia are also reversed by yawning. Yawning occurs with loss of interest (boredom) and may or may not be associated with fatigue. Pathological yawning in children and adults may have a hormonal or neurological basis.
De Vries distinguished the flowing types of fetal mouth movement: (1) jaw opening; (2) Yawning; (3) Sucking. In addition to these patterns, Van Woerden observed grimace and tongue protrusion movements. Most of these movernents were detected during behavioral states 1F (quiet sleep) and 2F (active sleep). The fetal mouthing movements were similar to those observed in neonates. Fetal yawning has been observed as early as 11 weeks of pregnancy, and most fetal yawning activity occurs during active sleep. None of the previously reported cases-of fetal yawning were associated with fetal hypoxia. Sepulveda and Mangiamarchi reported yawning in a 27-week healthy fetus and speculated that it may serve as a mechanism to protect against alveolar collapse in extrauterine life by expanding alveoli with inspired fluid during intrauterine life.
We observed yawning in healthy and high-risk fetuses. Studies of fetal yawning activity were performed as part of a protocol to study fetal behavior using a standard set-up (morning hours, quiet room, lateral recumbent position of the patient. The results of the first part of this study dealing with fetal swallowing have been published elsewhere.
Fetal yawning was a sporadic activity in the majority of fetuses studied, and this is in agreement with previous studies. Clusters of yawning activity were observed in our series in anemic fetuses. Although yawning should have no effect on P02 in intrauterine life as it does postnatally, it may change intrathoracic pressure, and thereby increase venous return to the heart. For this reason, the occasional yawning practiced by a normal fetus may be a compensatory mechanism in an anemic fetus.
Although a yawn is easily identified as such by observation of neonates or adults, the ultrasonographic identification of a yawn by a fetus has been called into question. McManus speculated that the image 'A fetal yawn', published in the New England journal of Medicine, may represent a single long-lasting opening of the mouth or a set of repetitive openings of the mouth lasting for 4-6 s and unrelated to yawning activity~ We agree that a single image is not enough to identify a particular pattern of behavior as a fetal yawn. However, if complex movements such as yawns are reliably identified in neonates, it is reasonable to assume that qualitative observational criteria can also be applied to fetuses to identify and characterize yawning. Continuous prolonged observation is necessary for proper identification and characterization of fetal yawning. Our initial experience with studying fetal yawning activity in healthy and abnormai fetuses is a descriptive study of a preliminary nature. One of the obvious problems with such a study is that one cannot be certain that all fetal mouthing movements are recorded; when the fetal is in the occiput anterior position the fetal face cannot be visualized adequately. Second, the large standard deviation for all three groups requires further study of larger numbers of hypoxic fetuses to ascertain whether observed differences between normal and abnormal patterns of yawning are significant.