Abstract : The aim of this study was
to investigate the characteristics of mouth
movements during behavioural states 1F (quiet
sleep) and 2F (active sleep) in the near term
human fetus. Thirty-six women participated.
Fetal heart rate and fetal movements were
recorded for 2 hours continuously. Videotapes
with enclosed periods 1F and 2F were replayed to
record fetal mouth movements in detail. During
1F, regular mouthing movements dominated
(present in 74%), while jaw opening, yawn and
grimace were only observed in 5 to 16% of the
recordings. Tongue protrusion was not observed
in 1F. In all 2F periods jaw opening was present
(100%), while tongue protrusion, yawn and
grimace were also frequently observed. Regular
mouthing was observed in 2F in only two fetuses.
For regular mouthing and sucking, onset-to-onset
intervals of clusters, cluster duration, and
number and frequency of movements within
clusters were calculated. In all aspects the
differences between these two types of movement
were statistically significant. Within the
clusters of regular mouthing a decline in the
mouthing frequency was found. The data on fetal
regular mouthing correspond with observations in
the neonate.
Introduction : Fetal mouth movments
can be observed with real-time echoscopy from 10
to 12 weeks onward. The following movments have
been descrided: jaw opening, yawn,
sucking and swallowing. Later in pregnancy a
typical movement pattern, called regular
mouthing, is visible: repeated small movements
of mouth or chin occurring in clusters. Another
type of fetal mouth movement occurring in a
rhythmical fashion is sucking. This movement
involves the buccal region, there is a larger
widening of the jaws than in regular mouthing
and it is sometimes followed by swallowing.
So far the temporal organisation of fetal
mouth movements has not been examined. This
paper describes the incidence of various types
of fetal mouth movement in the near-term human
fetus, in particular during the two most
prevailing fetal behavioural states 1F (quiet
sleep) and 2F (active sleep). The pattern of
fetal regular mouthing and sucking is analysed
in detail. [...]
Discussion: The temporal pattern of
the various discernable mouth has been described
and analysed within periods of C1F and C2F in
the near-term human fetus. During the C1F
periods the prevailing type of mouth movements
is regular mouthing. Other types of movement
only occur sporadically. During the C2F periods,
a wide variety of mouth movements is present,
with jaw opening being the most prominent.
In studies on the neonate the terminology
used for mouth movements with a rhythmical
pattern is confusing. The concept of rhythmical
or regular mouthing is commonly used for
spontaneous mouth movements occurring in
clusters. Other denominations are: spontaneous
non-nutritive sucking and spontaneous sucking
movements. Wolff, on the other hand,
distinguished spontaneous regular mouthing from
non-nutritive sucking (NNS) and nutritive
sucking (NS). The latter two movements were
studied with a blind nipple (in case of NNS) or
a nursing nipple (in case of NS), connected to a
pressure transducer. NNS was considered any
repetitive mouthing activity other than biting,
and appeared to cause changes in positive
pressure. NS was defined as any repetitive
mouthing activity on a nursing nipple associated
with negative intra-oral pressure sufficient to
deliver a potable fluid from that nipple.
Despite the muddle in terminology the results on
mouthing movements in these studies correspond
with our own. All authors report a frequency of
mouthing movements around two per second within
a cluster, similar to our results in the
fetus.
Wolff found the same mouthing rhythm with and
without a pacifier. The author described in his
study a decline in the sucking rate within
clusters of non-nutritive sucking. We found the
same phenomenon with regard to the pattern of
regular mouthing in the term fetus. This
supports the assumption that non-nutritive
sucking and regular mouthing are regulated by
the same mechanism in the central nervous
system. Probably the presence of a pacifier
elicits regular mouthing movements, which are
also performed spontaneously.
In the neonate, regular mouthing is most
frequently observed during state 1 (quiet sleep)
and is more rarely observed during state 2
(active sleep).Our results are in agreement with
these findings. As Wolff did in his study, we
found a slower mean frequency per second for
sucking compared to regular mouthing (1.4 + 0.2
vs. 2.5 + 0.2). The typical cluster
configuration of the sucking movements in the
fetus bas not been described by Wolff for the
nutritive sucking in the neonate: nutritive
sucking is organized as a continuous stream
rather than an alternation of bursts and rest
periods. In fact, the presence or absence of a
burst-rest configuration was directly related to
the absence or presence of milk flow. In this
respect the fetus differs from the neonate
(sucking does not have a nutritive function yet)
which could explain the discrepancy in sucking
pattern.
Among many other factors mouth movements. in
particular regular mouthing and sucking,
influence the fetal heart rate. During sucking
movements a sinusoidal-like heart rate pattern
appears. Regular mouthing is reflected in the
heart rhythm as an oscillatory pattern with a
mean frequency of 3 (SEM 0.15) per minute and a
mean amplitude of 9 (SEM 0.35) bpm. One of the
factors leading to decreased or absent heart
rate variability (the so-called silent heart
rate pattern) could be absence of regular
mouthing. Further studies are necessary to
assess the relationship between the pattern of
mouth movements in relation to heart rhythm and
behavioural states in compromised
fetuses.
