Chapter 19 Malpresentation and malpositions

David T Y. Liu

CHAPTER CONTANTS

Definitions 163

Malposition 163

Malpresentation 163

Associations 164

Labour 164

Deflexed head 164

Delivery 164

Occipitoposterior positions 164

Diameters for consideration 164

Types 164

Diagnosis 164

Palpation 164

Vaginal examination 165

Course of labour 165

Uterine activity 165

Gynaecoid and other adequate pelvis 165

Anthropoid (ellipsoid) pelvis 165

Android pelvis 165

Occipitoposterior position and deflexion of the head 165

Management 166

Face presentation 166

Types 167

Diagnosis 167

Primary face 167

Secondary face 167

Management 167

Mentoanterior position 167

Mentolateral position 167

Mentoposterior position 167

Brow presentation 168

Types 168

Diameters for consideration 168

Diagnosis 168

Primary brow 168

Secondary brow 168

Management 168

Compound presentation 168

Management 168

Parietal presentation 168

Anterior asynclitism 168

Posterior asynclitism 168

Shoulder presentation (transverse or oblique lie) 169

Diagnosis 169

Abdomen 169

Vaginal 169

Prognosis 169

Management 169

DEFINITIONS

Malposition

This describes a vertex presentation which is not in the fully flexed anterior position, for example a deflexed head, and occipitolateral and occipitoposterior positions. The occiput is the denominator. A higher incidence is seen in mothers of African and Chinese origin.

Malpresentation

This describes all presentations which are not vertex, for example: face, brow, shoulder and breech presentation.

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Associations

• Fetus: abnormal, large, preterm, multiple.

• Uterus: abnormal, polyhydramnios, poor uterine tone, pendulous abdomen.

• Pelvis: abnormal, disproportion (contracted or capacious pelvis).

Labour

During pregnancy attention is drawn to these complications when the fundal height does not correspond to gestational dates, the lie is not longitudinal or the fetal head is not engaged. The fetal head may appear large because it is abnormal, or is in malposition. Before, or following labour, some of these complications may resolve spontaneously.

Labour in these women may:

• in certain circumstances produce these complications as a secondary feature (rotation from occipital anterior)

• be complicated by early membrane rupture and risk of cord prolapse

• be prolonged or become arrested

• require medical intervention assisted delivery or caesarean section.

An experienced obstetrician should be called to confirm the diagnosis and then to decide about labour and supervise the mode of delivery.

Diagnosis of malpositions signals need to anticipate operative delivery.

DEFLEXED HEAD

This describes a vertex presentation where the fetal head is not fully flexed to present the most advantageous biparietal diameter of 9.5 cm. This situation arises when:

• the fetus is small in relation to the pelvis, e.g. preterm birth

• congenital abnormalities are present

• the dimensions of the pelvis are marginal. This is particularly likely in occipitoposterior positions

• fibroids or tumours interfere with normal labour.

Labour is prolonged or may be arrested. Deflexion can progress to a brow or face presentation.

Delivery

Labour may be delayed in the second stage. Delivery may require an episiotomy, manual flexion of the fetal head or the application of forceps.

OCCIPITOPOSTERIOR POSITIONS

These describe the situation where the occiput is in the posterior part of the pelvis. This position is found in 10–13% of all vertex presentations. Contributory factors include:

• a large baby

• an android or anthropoid (ellipsoid) pelvis

• pelvic brim contracture or flat sacrum

• anterior low-lying placenta

• a deflexed head

• malrotation.

Diameters for consideration

• Flexed occipitoposterior: presents the suboccipitofrontal which is 10 cm (Figure 19.1: b–c).

• Deflexed occipitoposterior: presents the occipitofrontal which is 11.5 cm (Figure 19.1: a–c).

Figure 19.1 Diameters for consideration in occipitoposterior positions: occipitofrontal (a–c) and suboccipitofrontal (b–c).

Types

• a)Right occipitoposterior (ROP) is the most common – the occiput lies opposite the right sacroiliac joint.

• b)Left occipitoposterior (LOP).

• c)Direct occipitoposterior – the occiput lies in the hollow of the sacrum (Figure 19.2).

Figure 19.2 Types of occipitoposterior position: ROP, LOP and direct OP.

Diagnosis

Palpation

The fetal limbs are anterior and give a hollowed appearance to the woman’s lower abdomen. The head is not engaged and the sinciput is felt superficial to the occiput on palpation when the woman is lying horizontally. The fetal shoulder and loudest heart sounds are located well lateral to the midline.

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Vaginal examination

The presenting part is poorly applied to the cervix. Deflexion is common. The anterior fontanelle is easily felt beneath the symphysis. If diagnosis presents difficulty, pass a finger alongside the fetal face and locate the ear. Running the fingers across the root of the ear will show that the pinna points in the direction of the occiput (Figure 19.3).

Figure 19.3 Palpating the ear as guide to direction of occiput.

Course of labour

This depends on the quality of uterine activity, whether disproportion is present and the type of pelvis.

Uterine activity

Strong regular contractions encourage flexion, engagement and rotation to an occipitoanterior position. Labour tends to be longer because the application of the presenting part of the fetus to the cervix is poor. In about two-thirds of such women, rotation through an arc of 135° from an occipitoposterior to an occipitoanterior position will be achieved (Figure 19.4). Extra time in labour is required to achieve this.

Figure 19.4 Rotation of occiput through the long arc (a) to deliver in the occipitoanterior position through the anteroposterior diameter of the outlet (b).

Gynaecoid and other adequate pelvis

Descent and flexion of the head occurs. Long rotation to the occipitoanterior position takes place at the level of the pelvic floor. Subsequently delivery is normal.

Anthropoid (ellipsoid) pelvis

Rotation to the occipitoanterior position is not favoured because the transverse diameter of the pelvis is narrow. The vertex rotates posteriorly a short distance, through 45° to deliver in the persistent occipitoposterior position. Deflexion is common, hence the presenting diameter is the wider occipitofrontal (11.5 cm) position. The head delivers by flexion followed by extension to allow the brow and the face to appear beneath the symphysis. The wider presenting diameter of the fetal head causes more trauma to the vagina, hence an episiotomy is necessary to prevent tearing. Assistance with forceps or ventouse extraction to complete the delivery is commonly required.

Android pelvis

Rotation to an anterior position becomes progressively more difficult with descent because the pelvis is narrow anteriorly, and the walls of the lower part of the android pelvis converge towards the outlet. Spontaneous rotation to an anterior position is possible if the pelvis diameters are adequate. In a marginal-sized pelvis, failure to rotate can occur at any level of the pelvis. The vertex can remain in the occipitoposterior position or rotation may be arrested with the head in the transverse position. When failure to rotate or descend occurs high in the pelvis, this situation is termed deep transverse arrest (DTA) (Figure 19.5). Delivery will require assistance.

Figure 19.5 Schematic illustration of increasing difficulty for rotation to occipitoanterior in an android pelvis.

Occipitoposterior position and deflexion of the head

In a marginal-sized pelvis partial deflexion will present wider fetal diameters and hence obstruction to progressive labour. With a capacious pelvis deflexion can produce a brow or face presentation.

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Management

• Ensure good uterine contractions.

• Provide adequate analgesia. Epidural analgesia is useful for long labours and operative delivery. Relaxation of the pelvic floor muscles may hinder anterior rotation.

• Assess the pelvic diameters carefully. If necessary use X-ray or magnetic resonance imaging to anticipate and evaluate any likely problems.

• Avoid maternal ketosis.

• Institute close fetal surveillance.

• Examine every 2–4 hours to assess progress. Failure to progress before full cervical dilatation necessitates caesarean section. Examine immediately after membranes rupture to exclude cord prolapse.

• If the presenting part of the fetus is on the perineum in an occipitoposterior position, it is acceptable and possibly safer to deliver as an occipitoposterior with the help of an episiotomy and forceps or ventouse extractor.

• When occipitoposterior or transverse position causes delay in the second stage the following procedures should be adopted:

• if the presenting part of the fetus is low down assist delivery by rotation to occipitoanterior or posterior position depending on the pelvic type and ease of manoeuvre

• if the presenting part of the fetus is at the mid-cavity, conduct a trial of forceps rotation and delivery with preparation for caesarean section in case of failure.

FACE PRESENTATION

The incidence of face presentation is 1 in 500 deliveries. The diameter for consideration is the submentobregmatic, which is 9.5 cm. The denominator is the chin or mentum which may be found in any one of eight positions (Figure 19.6). During labour the chin is the lowest point or leading part. Seventy-five per cent of face presentations are in the mentolateral or mentoanterior positions. Rotation in the lower half of the pelvis to the direct mentoanterior position usually occurs if the pelvis is adequate. The head is delivered by flexion. Assisted delivery is necessary for mentoposterior positions. Forceps rotation may be tried, but caesarean section is usually required for delivery (Figure 19.7).

Figure 19.6 Mentum (chin) in the right and left posterior, lateral and mentoanterior positions together with direct mentoposterior and mentoanterior.

Figure 19.7 Delivery of head in mentoanterior by flexion.

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Types

• Primary: face presentation before the onset of labour.

• Secondary: face presentation during the course of labour.

Diagnosis

Primary face

This is diagnosed when there is a non-engaged head, the head feels large or when the extended head is felt on the same side of the uterus as the fetal back. Radiology or ultrasound scanning is carried out to confirm suspicion. Assess adequacy of pelvis and exclude any abnormalities (fetal and maternal).

Secondary face

Suspect this diagnosis if the presenting part of the fetus appears low yet a large part of the head is palpable suprapubically. The eyes, nose, supraorbital and alveolar ridges, and the mouth can be felt on vaginal examination. Unlike the anus, the mouth does not grip the examining finger and firm fetal gums are felt. Ultrasound scan can confirm the diagnosis (Figure 19.8).

Figure 19.8 Face presentation provides a situation for a low presenting part with the impression of a non-engaged head.

Management

• Exclude any abnormalities. An ultrasound scan is useful.

• Assess carefully the size of the fetus and the pelvis. The face does not mould and safe vaginal delivery is not likely unless pelvic diameters are ideal.

• Ensure adequate analgesia; epidural analgesia is particularly useful.

• Maintain close surveillance. Fetal distress is likely because of the long labour and unfavourable neck positions.

Mentoanterior position

Labour is prolonged. The presenting part is poorly applied. The engaging diameter 9.5 cm (submentobregmatic) is at a lower level than the biparietal (9.5 cm) diameter. The diameter of 9.5 cm is thus presented twice at 90° to the cervix (Figure 19.9). In ideal conditions spontaneous delivery can occur. Usually an episiotomy and assistance with forceps is required for vaginal delivery. The ventouse extractor is contraindicated. Failure to progress in the first stage of labour necessitates a caesarean section.

Figure 19.9 Schematic illustration of presentation of diameter 9.5 cm twice to the cervix: once with submentobregmatic then with the biparietal.

Mentolateral position

In an adequate pelvis, expect rotation to the mentoanterior position and an assisted vaginal delivery. Rotation occurs at or below the level of the ischial spines. Manual or forceps rotation may be required. If the pelvic outlet is suspect or spontaneous rotation is arrested in mid-pelvis, deliver by caesarean section.

Mentoposterior position

Unless the fetus is very small or the pelvis capacious, the shoulder and vertex cannot be accommodated at the same time. Obstruction is inevitable. Attempting rotation to the mentoanterior position is seldom advised. Deliver by caesarean section. If the fetus is dead consider delivery by craniotomy and forceps (only if the operator is experienced). Facial oedema and bruising is usual.

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BROW PRESENTATION

Brow presentation has an incidence of approximately 1 in 2000 or more deliveries.

Types

• Primary: presentation before labour. The position is usually transient and reverts to the occipitoposterior or face positions when labour starts. Exclude fetal abnormalities and inlet disproportion.

• Secondary: develops during labour. This usually follows deflexion of an occipitoposterior position.

Diameters for consideration

The fetus presents by the mentovertical diameter (13.5 cm) which is greater than the largest pelvic diameter of 12.5 cm (Figure 19.10).

Figure 19.10 The mentovertical diameter in brow presentation.

Diagnosis

Primary brow

Abdominal palpation reveals a large non-engaged head. Exclude fetal abnormality and disproportion. Await onset of labour.

Secondary brow

Application to the cervix is poor. The presenting part may be felt high behind the bag of forewaters. The anterior fontanelle, supraorbital ridge and the nose can be felt. Confirm by ultrasound scan or radiology.

Management

• If the fetus is alive and of normal size, presentation by the brow can only be safely delivered by caesarean section. Unless practised expertise is available, manipulative correction of the presentation is seldom justified.

• If the fetus is small or preterm, spontaneous delivery can occur. If assistance is necessary convert the brow to a face (mentoanterior) or occipitoposterior position before delivery by forceps.

COMPOUND PRESENTATION

This describes a situation when the hand or forearm accompanies the presenting part of the fetus. It is usually associated with poor application of the presenting part and a small or preterm infant in a large pelvis.

Management

• If compound presentation is found during labour, the hand can be pushed up behind the presenting part.

• If this is not possible, await full cervical dilatation, ensure adequate analgesia, disimpact the limb and deliver by forceps or ventouse extraction.

• If prolapse of the whole forearm obstructs labour, caesarean section is required.

PARIETAL PRESENTATION

In a flat pelvis the vertex engaging in the occipitolateral position will have to tilt (attitude of asynclitism) sideways to swivel past the sacral promontory and the symphysis.

Anterior asynclitism

This is when the parietal eminence in front tilts behind the symphysis. This is a favourable presentation and once the biparietal eminences swivel past the sacral promontory and symphysis, rotation to occipitoanterior or posterior is the usual course (Figure 19.11).

Figure 19.11 Anterior asynclitism illustrating position of fetal body to assist entry of the biparietal diameter into the pelvis.

Posterior asynclitism

This is when the parietal eminence at the back enters the pelvis first by slipping past the sacral promontory. This is less likely to succeed because unlike anterior asynclitism in which the fetal body can lean anteriorly to assist engagement of the anterior parietal eminence, in posterior asynclitism the mother’s spinal column prevents this action of the fetal body. Failure of either anterior or posterior asynclitism to engage the fetal head means that caesarean section is necessary for delivery (Figure 19.12).

Figure 19.12 Posterior asynclitism illustrating restriction of fetal body movement to assist entry of biparietal diameter into pelvis.

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SHOULDER PRESENTATION (TRANSVERSE OR OBLIQUE LIE)

In both transverse and oblique lie, the shoulder is the most common presenting part. In an oblique breech the ilium may present. The causes of shoulder presentation are listed in Table 19.1.

Table 19.1 Causes of shoulder presentation

Maternal	Fetal
Relaxed multigravid uterus (most common cause)	Abnormality Twins
Pelvic contracture	Prematurity
Uterine abnormality	Fetal death
Obstruction by intra or extrauterine masses	Polyhydramnios Placenta praevia

Diagnosis

Abdomen

The fundal height appears small for dates (unless there is multiple gestation or polyhydramnios). The uterus appears broad with fullness in the flanks. No presenting part is palpable in the pelvis. The head or breech is felt opposite the iliac crest or at right angles to the mid-line.

Vaginal

No vaginal examination should be performed until placenta praevia is excluded. Avoid membrane rupture and risk of cord or arm prolapse. If the membranes have ruptured, examine immediately to exclude cord prolapse. The pelvis feels empty with the ilium and/or shoulder presenting. The fetal ribs give a characteristic ‘washboard’ feel.

Prognosis

This is a dangerous situation for both the fetus and the mother. Spontaneous delivery is not possible unless the fetus is very small. The risk of cord prolapse, shoulder impaction, uterine rupture and the need for classical caesarean section all increase maternal and fetal mortality and morbidity.

Management

• The onset of labour with increased uterine tone may rectify the situation and convert an oblique to a longitudinal lie. This is most likely in a multigravid mother with a lax uterus.

• Identify the cause of malpresentation. Radiology or sonar examination is useful.

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• Elective caesarean section is performed if vaginal delivery is contraindicated. This applies to the majority of primigravid mothers.

• If the mother is not in labour and vaginal delivery is suitable:

• manoeuvre fetus (external version) to longitudinal lie. This is performed in a theatre prepared for caesarean section

• set up intravenous oxytocin to generate and maintain uterine contractions

• perform amniotomy, drain liquor slowly and guide the presenting part into the pelvis.

• If the mother is in early labour with ruptured membranes perform vaginal examination to exclude prolapse of the limbs or cord.

• Attempt to encourage a longitudinal lie if vaginal delivery is considered possible. If this is not successful deliver by caesarean section. A midline abdominal incision followed by a low vertical incision in the uterus is advised when fetal lie is fixed. Convert the vertical uterine incision to a classic incision if necessary.

• Impacted shoulders – whether the fetus is alive or dead, deliver by caesarean section. Destructive procedures in inexperienced hands may result in uterine rupture.

• Spontaneous expulsion of the fetus can only occur if the fetus is macerated or is very small.

Bibliography

Gardber GM, Tuppurainen M. Persistent occiput posterior presentation – a clinical problems. Acta Obstetrica et Gynecologica Scandinavica. 1994;73:45-47.

Gardber GM, Laakkonen E, Salevarra M. Sonography and persistent occiput posterior position:a study of 408 deliveries. Obstetrics and Gynecology. 1998;91:746-749.

Holmberg NG, Lilieqvist B, Magnusson S. The influence of the bony pelvis in persistent occiput posterior position. Obstetrica et Gynecologica Scandinavica Supplement. 1977;66:49-54.

To WW, Li IC. Occipital posterior and occipital transverse positions: reappraisal of obstetric risks. Australian and New Zealand Journal of Obstetrics and Gynaecology. 2000;40:275-279.