Malpresentations and Malpositions

Causes

• Fetal anomalies are found in about 15% of face presentations. The commonest are major CNS anomalies such as anencephaly and meningomyelocoele. Tumours of the neck may also cause extension and face presentation.

• Prematurity.

• It is possible that in some cases of deflexed occipitoposterior position with relative disproportion the fetal head may extend completely to a face presentation.

• More common in women with high parity

• In most cases, other than parity, no obvious cause is found.

Diagnosis

The presenting part of the face is between the chin and supraorbital ridges. Usually the characteristic landmarks of the eyes, nose, mouth and chin can be felt with the examining finger during labour. Considerable oedema often develops which may, to a degree, obscure these landmarks. Although the distinction is usually obvious there may be confusion in distinguishing between the mouth and the anus. If this is so, the finger is inserted into the orifice and the gum ridges can easily be felt as a distinguishing landmark.

Diagnosis before labour is rare. If there is clinical suspicion, ultrasound will establish or refute the diagnosis.

The position of a face presentation is defined with the chin as the denominator and is therefore recorded as mentoanterior, mentoposterior or mentotransverse, left or right accordingly. The majority of cases are mentoanterior.

Management

On the rare occasions that face presentation is diagnosed before labour, a careful ultrasound examination should be made to exclude structural fetal anomalies. One can make the case for observation until the onset of labour or full term, on the grounds that a number of these cases will revert spontaneously to a normal flexed vertex position. However, if face presentation persists and the fetus is normal, it should be delivered by elective caesarean section.

When the diagnosis is made in labour, a gross fetal anomaly should be excluded and clinical pelvimetry should rule out obvious pelvic contraction or deformity. The position of the face presentation is then assessed. Depending upon the estimated fetal weight, the position, station, clinical assessment of pelvic capacity and the progress of labour, the following principles may be helpful.

If the fetus has an anomaly incompatible with life then a vaginal delivery should be considered to avoid unnecessary maternal intervention.

If the position is mentoanterior, which presents the same diameters as a flexed vertex, if the fetus is normal or small in size, the pelvis is of good capacity and progress in labour is adequate then it would be reasonable to consider a normal delivery. The majority of cases with mentotransverse position will rotate to the more favourable anterior position. Oxytocin to accelerate or induce labour should not be used.

Provided labour continues normally and there is good progress in the second stage with mentoanterior positions, spontaneous delivery is likely.

If progress is inadequate with mentoanterior positions, consideration of forceps delivery is appropriate but the face should be on the perineum and delivery take place vaginally only if a simple lift out delivery is anticipated and it is clinically safer than performing a caesarean section.

In cases of mentoposterior position which do not rotate to anterior during labour, vaginal delivery is impossible ( Fig. 14.3 ).