INTRODUCTION 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.
METHODS 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.
RESULTS 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.
DISCUSSION 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.
