Malpresentation and malposition

Published on 09/03/2015 by admin

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Chapter 39 Malpresentation and malposition

Michael Flynn

Stages of labour

Labour is divided into three stages:

• The first stage commences with painful contractions, which dilate and efface the cervix. This stage ends with full dilatation of the cervix, and is further divided into the latent and active stage. The active stage begins at full effacement of the cervix.
• The second stage begins at full dilatation and ends with the delivery of the baby.
• The third stage ends when the placenta is delivered.

At term, about 95% of fetuses are cephalic in presentation. Of these, up to 95% will deliver in the occipito-anterior position. Malpresentations and malpositions increase the maternal risks of prolonged labour, infection, obstructed labour, tissue necrosis resulting in vesico/rectovaginal fistulas, and deep venous thrombosis. Fetal risks of malpresentation and malposition are cord prolapse, traumatic delivery and hypoxia.

Occipito-posterior position

The fetal head usually engages in the lateral position, and in 80% of cases it rotates anteriorly. About 20% of fetuses are in the occipito-posterior position in early labour (usually occiput to the right). With increasing flexion in labour, there is a tendency for the fetal head to rotate when it reaches the pelvic floor.

Risk factors for persistent occipito-posterior position

• anterior placenta
• anthropoid or android pelvis, where the pelvic brim is longer in the anterior–posterior diameter than in the transverse
• inefficient uterine contractions

Diagnosis

The occipital bone is the only bone that is overridden by its neighbours. When the diamond-shaped anterior fontanelle can be palpated on vaginal examination, this indicates deflexion of the fetal head.

The maternal abdomen appears flat below the umbilicus, and fetal limbs can be palpated anteriorly on the maternal abdomen.

Characteristics of labour

• The woman complains of backache.
• There is a tendency for incoordinate uterine action and prolonged labour.
• There is early distension of the perineum and dilatation of the anus, while the fetal head is high in the birth canal.

Management

• Slow progress in the first stage of labour often requires oxytocin augmentation.
• In the second stage, adequate uterine contractions are required for rotation of the fetal head on the pelvic floor. Occasionally, the fetus will spontaneously deliver in the occipito-posterior position.
• An instrumental delivery may be indicated for a prolonged second stage. Vacuum extraction, using the posterior cup position, will encourage flexion and rotation of the fetal head to correct the relative disproportion. Kielland’s rotational forceps may also be used.
• Delivery by caesarean section is indicated if the station of the head is above the ischial spines.

Face presentation

Risk factors

• Fetal factors include anencephaly, cystic hygroma, goitre, prematurity and multiple pregnancy.
• Maternal factors include bicornuate uterus and pelvic tumours.

Diagnosis

Most are diagnosed in labour just before delivery. Up to 75% are in the mento-anterior position. The landmarks at vaginal examination are the mouth, jaw, nose, malar and orbits. The mouth and maxilla form a triangle.

Management

Aim for a vaginal delivery, especially if the baby is in the mento-anterior position. However, if the baby is in the mento-posterior position and there is failure to rotate, the baby cannot be delivered vaginally and caesarean section is required.

Brow presentation

Incidence. Incidence is about 1 in 1000 deliveries.

Risk factors

• fetal: as with face presentation
• maternal: contracted pelvis

Diagnosis

• Vaginal examination: this includes palpation of the anterior fontanelle and orbital ridges.
• Labour in the brow presentation is often prolonged and obstructed.

Management

• No treatment is necessary if diagnosed in early labour and progress of labour is adequate. The baby may deflex to a face presentation or flex to a vertex presentation.
• Perform caesarean section if there is delay in labour or disproportion.
• Instrumental delivery may be attempted if the cervix is fully dilated and there is no clinical evidence of cephalopelvic disproportion.

Transverse and oblique lie

Incidence. Incidence is about 1 in 300 deliveries.

Risk factors

• fetal: prematurity, multiple pregnancy, polyhydramnios, fetal death and placenta praevia
• maternal: multiparity, contracted pelvis, pelvic tumours and abnormal uterine shape

Diagnosis

• Uterus is small for dates; there is no fetal pole in fundus or pelvis.
• Confirm the diagnosis by ultrasound examination.

Labour

• It is often incoordinate and obstructed.
• Uterine rupture may occur and there is a risk of cord prolapse in 10%–15% of cases.

Management

• If the unstable lie persists over 37 weeks, admit the woman to hospital and await labour. If the unstable lie persists after 38 weeks or labour commences, caesarean section is indicated.
• Internal version of the fetus may result in uterine rupture, and this is indicated only for a second twin.

Cord prolapse and presentation

Incidence. Incidence is about 1 in 200–300 deliveries.

Risk factors

• poorly applied presenting part
• fetal: prematurity, long umbilical cord, low-lying placenta
• maternal: multiparity
• iatrogenic: operative manoeuvres, including artificial rupture of membranes and forceps delivery

Management

• Advise the woman to present as soon as possible when membranes rupture, especially women with risk factors.
• When a cord presentation is diagnosed, the presenting part must be pushed away from the cord to avoid cord compression, and immediate delivery of the baby is required.

Diameters of presenting parts

• occipito-anterior = suboccipito-bregmatic = 9.5 cm
• occipito-posterior = occipito-frontal = 11 cm
• face presentation = submento-bregmatic = 9.5 cm
• brow presentation = mento-vertical = 14 cm

Further reading

Ritchie J.K. Malpositions of the occiput and malpresentations. In Dewhurst’s textbook of obstetrics and gynaecology for postgraduates. Oxford: Blackwell Scientific; 1998.

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