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7/25/2019 Unstable Lie ZUAR 11
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Unstable Lie, Malpresentations,
and Malpositions
INDTRODUCTION
Near team and during labor, the fetus normally
assumes a longitudinal lie and present with the cephalic
pole to the maternal pelvis with the neck flexed and the
vertex in the lowermost part of the uterus. In
approximately 5% of labors, lie is not longitudinal. This
is usually associated with dangers to both mother and
fetus demands intervention. s with much of medicine,
the prior identification of the pregnancy at particular
risk of an unstable lie, malpresentation, or malpositioncan allow intervention in advance of a complication
developing and improve the outciome for the mother
and baby. This chapter will not consider issue relating
to fetal breech presentation as these are dealt with
elsewhere !see "hapter #$.
DEFENITIONS
Unstable Lie
This is a description generally used beyond &'
weeks( gestation when the fetal lie and presentationrepeatedly change, the lie varying from longitudinal, to
transverse, and obli)ue, and the presentation from
cephalic, to back, limbs, breech or a combination. *y
&' week the fetus usually adopts a +stable lie and a
presentation that will be unchanging until labor and
delivery. The fetal position, describing the relationship
of the fetal back to the maternal side may, however,
change.
Malpresentation Including Compound resentation
This refers to the fetus that does not present tothe maternal pelvis by the vertex alone. The presenting
part is defined as that part of the fetus that is lowermost
in the uterus. lternatives include face, brow, breech,
and shoulder, as well as compound presentations thatinvolve more than one fetal part, including a
combination of the haed or breech with a limb or limbs
or umbilical cord or a combination of limbs with or
without the umbilical cord.
Malposition
fetal malposition refers to when the fetal
vertex present to the maternal pelvis in a position other
than flexed in a accipitoanterior position. -alposotions
include occipitotranserve and occipitoposterior
positions and may involve some degree of asynclitism
!sideways tlit of the head.
igure #5/0 is an illustration of the various
positions that the vertex and brow or face may adopt
during labor.
ETIOLO!"
Unstable Lie
1nstable lie is much more common in parous
than nulliparous women, but may be caused by or
associated with a number of factors. ny situation that
discourages or prevent the fetal head or breech from
entering the maternal pelvis will predispose to an
abnormal and unstable fetal lie. igure #5/2 illustrates
some of the factors associated with an unstable fetal lie.
Maternal Factors
3I43 6IT7
Increasing muscle laxity in the maternal anterior
abdominal wall so that it fails to act as a brace and
encourage and maintain a longitudinal fetal lie is
probably the most fre)uent associated factor. In
addition, there is a commonly held view that the highly
parous urterus has reduced myometrial tone, thereby
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encouraging an unstable lie, this has not been proven
and is of doubtful relevance.
L#CENT# RE$I#
persistently changing fetal lie may be the only
clinical feature leading to the diagnosis of placenta
previa. In addition, a placenta situated in the fundus
may also predispose to an unstable lie.
EL$IC TUMORS
8varian cysts and low/lying fibroids can obstruct the
fetal head or breech entering the pelvis and may result
in a high head or breech and transverse or obli)ue lie.
UTERINE M#LFORM#TION
1terus cordiformis, subseptus, or septus may be
causative. -ore severe forms of uterine anomaly,
including uterus bicornis and uterus didelphys, are less
likely to lead to an unstable lie due to the restricted
uterine capacity9 a predisposition to fetal breech
presentation, however, result.
DISTENDED MATERNAL URINARY
BLADER
-aternal urinary retention with a distended bladder can
cause a changing fetal lie, usually only temporarily,
with resolution occurring with urinary voiding or
bladder catheteri:ation.
Fetal Factors
8;737
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unstable lie and is also potentially the most ha:ardous
for mother and fetus !see "hapter 0&.
8;I48337 6>4NN"7
The discovery of an abnormal lie during the last three
week of pregnancy may arouse suspicion of a multiple
pregnancy and lead to investigations hat result in the
diagnosis being reached9 nowadays such a diagnosis is
unlikely to have been missed until this stage of
pregnancybecause of the widespread use of routine
ultrasonography during the early weeks of gestation.
?hen the lie of one both fetuses repeatedly changes,
there is usually polyhydramnios.
>T; -"68=8-I
etal macrosomia produce the same effect as pelviccontracture and must also be considered in such cases.
>T; *N86-;ITI>=
=ignificant hydrocephaly, tumors of the fetal neck or
sacrum, fetal abdominal distension as occurs with
hydrops fetalis, and fetal neuromuscular dysfunction
!including extended legs may impede or discourage
engagement of a fetal pole in the maternal pelvis. In
cases of intrauterine death, the fetus is more likely to
present abnormally due to loss of tone, sometimes even
re)uiring delivery by cesarean section because vaginal
delivery is impossible.
Compound resentation
"ompound presentation are most usually associated
with polyhydramnios and high parity and are more
common during the early weeks of the third trimester.
-ultiple pregnancies especially those that are
monoamniotic, represent a particular risk. elvic
tumors, including uterine fibroids low in the uterine
body or an ovarian cyst situated in the pouch of
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determining the position and attitude of the fetal head.
s well as uterine contraction strength being important,
there is now good evidence that the tone of the pelvic
floor is also relevant. 1se the regional anesthesia for
the management of pain relief during labor has been
implicated as a mechanism for the increased rates of
malposition in late labor although this is disputed.
6egional anesthesia provides an extremely effective
method of reducing the distress of labor, distress that is
more common with a preexisting occipitoposteriorposition. The issue of cause and effect thus comes into
play. The experience reported from
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examination when the maternal pelvis is large and the
interloping limb with the head or breech does not delay
engagement of the presenting part.
"ompound presentations involving the umbilical cord
are usually classified according to Neagele, who
distinguished between +presentation before membrane
rupture and +prolapse after membrane rupture.
diagnosis of cord presentation will not usually be made
prior to the onset of labor except in those cases of anunstable lie when a vaginal examination is performed
as part of the assessment of the strategy for continued
management. lthough some have documented
reaching the diagnosis with ultrasound, this is not a
widely reported observation.
Face resentation
8lder texts report that abdominal palpation allows the
diagnosis of a fetal face presentation to be made by the
recognition of a much broader lower pole presenting to
the pelvis than usual and the palpation of a marked
depression between the fetal back and occiput !ig. #5/
&. This is more easily demonstrated if the fetus is lying
in a dorsoanterior, or mentoposterior presentation this is
less common than a mentoanterior presentation. It is
also said that the fertal heart sound are very easily
heard when listened to over the fetal chest, especially
with a mentoanterior position9 this potentially valuable
clinical sign is lost if hand/held
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rupture is high if labor in a parous woman is notprogressing and is left to continue for too long.
Malpositions
ew risk are associated with a fetal malposition prior to
labor. s already stated, there is a belief that prelabor
rupture of the membrane is more common with an
occipitoposterior position. =ince the head usually not
engaged and may not be well settled into the pelvis, the
risk of cord prolapsed is increased.
8nce in labor, progress may be slower than
with an anterior position, and maternal distress is often
increased, with discomfort felt particularly in the back.s well as a protracted first stage of labor, there is often
a delay during a second stage with the need for
augmentation of contractions with exytocin, or
assistance with manual rotation, forceps delivery with
or without rotation, or assistance with the ventouse.
?ith a current reluctance to engage in rotational
procedures, especially if fetal distress is suspected,
there is an increased risk of cesarean section.
It as recently been shown by one group that the
occipitoposterior position that persist to the time ofvaginal delivery present a significant risk of anal
sphincter damage for both nulliparae and multiparae.
M#N#!EMENT
Unstable Lie and Compound resentation
Antenatal
6G>NTI8N
8nce an unstable lie is identified, no specific action is
taken in anticipation that the lie will become
longitudinal before the membranes rupture or labor
starts9 this is likely to occur in more than CA% of cases.
-anipulation to a longitudinal lie at an antenatal
examination can sometimes be performed. >very
attempt should be made to identify any obvious
mechanical cause for the unstable lie, especially if it
likely to result in obstructed labor, thus re)uiring
elective cesarean section. The patient should be advised
of the risk associated with an unstable lie and the need
for urgent attention should labor start or the membranes
rupture. If the women lives very far from the delivery
unit, it may be necessary to admit her from about &'
weeks to await the onset of labor to ensure prompt
attention at the onset of labor.
number of physical exercises, such as the women
adopting the knee/elbow position for short periods on a
number of occasions each day, have been advocated to
promote spontaneous version, generally from a breechto chepalic presentation. =uch maneuvers possibly
improve the chances of a longitudinal lie by 5% to
0A%, but there is no established evidence base for this
proposition.
INTER$ENTION
dmission may be advised from &' to &D weeks
gestation onward. this enables daily observation of fetal
lie and presentation to be made9 provides to opportunity
for active treatment to correct the lie if necessary9
allows for immediate clinical assistant upon membrane
rupture or the onset of labor9 and facilitates urgent
management if the lie is not longitudinal, fetal distress
occur,, or the cord is presenting or prolapsed.
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In the event of continuing unstable lie, a
stabili:ing induction may be performed, either
immediately following admission or when an
appropriate gestation !usually &C/&D weeks has been
reached during the following days or weeks. ollowing
transfer to the labor suite an external cephalic version is
performed converting the fetal lie to longitudinal. 8nce
in position, regular abdominal palpations are performed
to confirm the longitudinal lie ismaintained and atitrated intravenous infusion of oxytocin is commenced
to stimulate uterine contractility. s soon contractions
are occuring at 0A minute intervals or more fre)uently,
a low amniotomy is performed, having ensured the lie
is still longitudinal and the presentation is not
compound and in particular that the cord is not
presenting. If the cord presents, an emergency cesarean
section is necessary. 8nce low amniotomy is
performed, a reasonable volume of amniotic fluid
should be released, followed by confirmation that thecord is not presenting and the presenting part is fixed in
the pelvic brim. Thereafter, once labor is established,
management continues as for an uncomplicated labor.
hindwater amniotomy using a
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succesfull, delivery should be achieved b cesarean
section9 attempts at version should only be performed
when immediate resort to section is available.
ALREADY RUPTURED MEMBRANES AT
FULL DILATATION
If the fetus is in a transverse or obli)ue lie or there is a
compound presentation, delivery should be performed
as urgently as possible, using the classical cesarean
section incision unless an attempt at external version
can be successfully made on opening the abdominal
wall and immediately before the uterine is incised.
transverse incision in the lower uterine segment is
likely to be inade)uate for fetal extraction because the
loss of amniotic fluid reduces the surgeon(s ability to
manipulate the fetus within the uterus. =truggling to
deliver the fetus through a lower segment incision can
cause serious trauma to the fetus, uterus, or both9 or the
uterine incision will need to be extended as an inverted
T or as a 1/shape incision. =uch incision extensions
may result in compromised healing and a vulnerable
area of scar integrity, which may predispose to uterine
rupture in future labors.
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Malpresentation
#ntenatal
8nce an identifiable specific causefor the
malpresentation has been diagnosed, treatment of the
precipitating condition may be incated !see relevant
chapter. or those cases without identifiable cause,
there are no recogni:ed and universally accepted
managements to adopt for correcting a fetal brow orface presentation. In view of the increased risk of cord
presentation and thus cord prolapse, the patient should
be advised of early admission when labor starts or
membrane rupture occurs.
s with an unstable lie, admission from &D
weeks( gestation shouldbe considered for this reason. If
delivery is indicated for other reasons, planned cesarean
section without recourse to labor may be a safer option
that inducing labor if there is a high presenting fetal
part. The alternative is labor induction with either localprostaglandins or intravenous oxytocin and low
amniotomy once contractions are established and the
fetal head fixed or engaged in the pelvic brim.
reparation should have been made to allow for rapid
cesarean section should cord presentation or prolapse
be diagnosed, with the patient forewarned of this
possibility.
Intrapartum
;abor management should be the same as for a vertex
presentation, assuming routine maternal and fetalobservation are satisfactory and good progress is
maintained E many brow presentations convert to a face
or vertex and the ma@ority of face presentations present
as mentoanterior. 8xytocin augmentation is acceptable
if uterine contractions are inade)uate, but caution
should always be shown since labor may become
obstructed with dire conse)uences if left unattended. If
progress in labor is slow, resort to cesarean section may
be a wiser option. igure #5/D illustrates the
management options
8nce full dilatation is reached with a
brow presentation, spontaneous delivery will
not folllow unless the fetus is very small or the
pelvis is unusually capacious. roviding the
assessment of the pelvis indicates that there is
no evidence of absolute disproportion, the
presentation can be converted with rotational
forceps to face or vertex, whichever proves to
be the easier, and then delivered. =ome have
advised the use of the ventouse in this situation
but thid re)uires the cup to be applied behindthe bregma and this is unlikely to be possible in
the ma@ority of cases. The current ma@ority
view is that unless the head is engaged in the
pelvis at the start of vaginal manipulations,
delivery by cesarean section is recommended.
?ith a face presentation, vaginal delivery
should be anticipated if the head is engaged, with the
delivery occuring spontaneously or assisted with
forceps. The head should be a mentoanterior position at
the delivery, achieved by forceps rotation if necessary
!see chapter '$. The ventouse has no place in the ...
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management of a face presentation. Thus cesarean sec
tion complete the delivery may be necessary if the
obstetrician dose not have the necessary skills to
conduct a rotational forceps procedure.
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Malposition
#ntenatal
There is probably little benefit from trying to alter an
occipitoposterior position diagnosed during the
antenatal period because the ma@ority of cases correct
themselves once labor starts. There may be some virtue
in advising the patient that her membranes may rupture
prior to the onset of contractions, that labor may be
more uncomportable and possibly more prolonged, and
that there is a greater chance of re)uiring assistance
with a vaginal delivery and need for delivery by
cesarean section, when compared with a more optimal
position. =ome women say that they find difficult labor
easier to cope with if forewarned, and they may be
more inclined to choose an epidural early in labor. 8n
the other hand, many occipitoposterior positions will
correct spontaneously to occipitoanterior during labor,
in which case anxiety will have been generated to no
purpose, and it may increase the likelihood of maternal
re)uest for delivery by elective cesarean section. =ome
have sugested the patient adopts a variety of positions
to encourage rotation of the fetus. n analysis of the
literature, concetranting on the use of the maternal
handskness position during the antenatal andintrapartum periods, concluded that this position
compared with others resulted in a short/term reversion
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to an anterior position. There was no indication that this
maneuver enhanced labor outcome, however.
Intrapartum
?hen the diagnosis of malposition is made early labor,
as much information as possible should be gathered at
this time about the fetal position, including the amountof head palpable per abdomen, the degree of deflexion
and asynclitism, the amount of molding and caput
formation, the level of the presenting part in relation to
the ischial spines, and maternal pelvis si:e and shape.
Issues relating to fetal well/being including fetal heart
rate patern and the color of the li)uor should also be
taken into account as with any labor.
8ption at thispoint are as illustrated in the algorithm
!see fig. #5/D and include
No specific action if acceptable progress is
being made.
rovide oxytocin augmentation if uterine
contractions are incoordinate, infre)uent, or of
poor )uality.
bandoning labor in favor of cesarean section.
>ncouraging the patient to lie on the same side
as the fetal back.
8nce the second stage of labor has been reached,
spontaneous delivery in the occipitoposterior
position may occur, or spontaneous rotation may
still occur with spontaneous delivery asoccipitoanterior. lternatively, delivery may be
delayed by a persistence of the occipitoposterior
position or the evolution of a deep transverse arrest.
It has been suggested that vaginal manipulation to
rotate the fetus to an occipitoanterior position
should be avoided if fetal distress is suspected at
that time, with resort instead to delivery by
cesarean section. The decision on management at
this stage should be determined by assessing which
method of delivery is most likely to result in earlier
delivery.
UNST#%LE LIE #ND COMOUND
RESENT#TIONS
fetal or uterine abnormality can be responsible
for the changing lie and compound presentation.
The risk of complications such as cord prolapse and
uterine rupture exists whwn the membranes rupture
or once contractions begin.
=ome of the risks can be reduced by antenatal
admission with action to correct the lie or deliver
by cesarean section before labor.
The most significant risk when the membranes
rupture or labor starts is umbilical cord prolapsed.This usually mandates delivery by cesarean
section , but replacement of the cord is sometimes
possible and should be considered.
>xternal or internal version at full dilatation should
be considered if the lie is transverse or obli)ue and
the membranes are intact.
If there is a compound presentation with ruptured
membranes, cesarean section is usually necessary,
and a classical incision may be needed.
MALPRESENTATION AND MALPOSITION
primary face precentation may indicate a fetalabnormality and warrants appropriate investigation.
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In general,a fetus with a persistent brow
presentation cannot be delivered vaginally, but
conversion to vertex or face at full dilatation should
be considered unless pelvic disproportion is
anticipated.
etuses with a face presentation can deliver
vaginally in a mentoanterior position.
etuses with a face occipitoposterior position at full
dilatation may deliver spontaneously
occipitoanterior or posterior, re)uire an assisted
delivery occipitoposterior, or be rotated and
delivered occipitoanterior , or may need to be
delivered by cesarean section.
deep transverse arrest can usually be delivered
vaginally by rotation and assisteddelivery.
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UNST#%LE LIE #ND COMOUND RESENT#TIONS
fetal or uterine abnormality can be responsible for the changing lie and compound presentation.
The risk of complications such as cord prolapse and uterine rupture exists whwn the membranes
rupture or once contractions begin.
=ome of the risks can be reduced by antenatal admission with action to correct the lie or deliver
by cesarean section before labor.
The most significant risk when the membranes rupture or labor starts is umbilical cord prolapsed.
This usually mandates delivery by cesarean section , but replacement of the cord is sometimes
possible and should be considered.
>xternal or internal version at full dilatation should be considered if the lie is transverse or
obli)ue and the membranes are intact.
If there is a compound presentation with ruptured membranes, cesarean section is usually
necessary, and a classical incision may be needed.
M#LRESENT#TION #ND M#LOSITION
primary face precentation may indicate a fetal abnormality and warrants appropriate
investigation.