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.

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.

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.

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