Fetal Circulation Physiology and Features

 FACE PRESENTATION

Face Presentation: When the attitude of the head is one of complete extension, the occiput of the fetus will be in contact with its spine and the face will present. The incidence is about ≤1:500 and the majority develop during labour from vertex presentations with the occiput posterior; this is termed secondary face presentation. Less commonly, the face presents before labour; this is termed primary face presentation. There are six positions in a face presentation; the denominator is the mentum and the presenting diameters are the submentobregmatic (9.5 cm) and the bitemporal (8.2 cm)

Causes of Face Presentation

Anterior obliquity of the uterus

The uterus of a multigravida with slack abdominal muscles and a pendulous abdomen will lean forward and alter the direction of the uterine axis. This causes the fetal buttocks to lean forwards and the force of the contractions to be directed in a line towards the chin rather than the occiput, resulting in extension of the head.

Contracted pelvis

In the flat pelvis, the head enters in the transverse diameter of the brim and the parietal eminences may be held up in the obstetrical conjugate causing the head to become extended such that a face presentation develops. Alternatively, if the head is in the posterior position with the vertex presenting, and remains deflexed, the parietal eminences may be caught in the sacrocotyloid dimension of the maternal pelvis so that the occiput cannot descend, and the head becomes extended resulting in a face presentation. This is more likely in the presence of an android pelvis, in which the sacrocotyloid dimension is reduced.

Hydramnios (polyhydramnios)

If the vertex is presenting and the membranes rupture spontaneously, the resulting rush of an excess of amniotic fluid may cause the head to extend as it sinks into the lower uterine segment.

Congenital malformation

Anencephaly can be a fetal cause of a face presentation. In a cephalic presentation, because the vertex is absent the face is thrust forward and presents. More rarely, a tumour of the fetal neck may cause extension of the head.

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Antenatal diagnosis of Face Presentation

Antenatal diagnosis is rare since face presentation develops during labour in the majority of cases. A cephalic presentation in a known anencephalic fetus may be pre-sumed to be a face presentation.

Intrapartum diagnosis

Abdominal palpation

Face presentation may not be detected, especially if the mentum is anterior. The occiput feels prominent, with a groove between the head and back, but it may be mistaken for the sinciput. The limbs may be palpated on the side opposite to the occiput and the fetal heart is best heard through the fetal chest on the same side as the limbs. In a mentoposterior position the fetal heart is difficult to hear because the fetal chest is in contact with the maternal spine.

Vaginal examination

The presenting part is high, soft and irregular. When the cervix is sufficiently dilated, the orbital ridges, eyes, nose and mouth may be felt. However, confusion between the mouth and anus could arise. The mouth may be open, and the hard gums are diagnostic with the possibility of the fetus sucking the examining finger. As labour progresses the face becomes oedematous, making it more difficult to distinguish from a breech presentation. To determine the position the mentum must be located. If it is posterior, the midwife should decide whether it is lower than the sinciput, and if it can advance, it will rotate forwards. In a left mentoanterior position, the orbital ridges will be in the left oblique diameter of the pelvis. Care must be taken not to injure or infect the eyes with the examining finger.

Mechanism of a left mentoanterior position

• The lie is longitudinal.

• The attitude is one of extension of the fetal head and neck.

• The presentation is the face.

• The position is left mentoanterior.

• The denominator is the mentum.

• The presenting part is the left malar bone.

Extension

Descent takes place with increasing extension. The mentum becomes the leading part.

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Internal rotation of the head

This occurs when the chin reaches the pelvic floor and rotates forwards 1/8 of a circle. The chin escapes under the symphysis pubis

Flexion

This takes place and the sinciput, vertex and occiput sweep the perineum; the head is born.

Restitution

This occurs when the chin turns 1/8 of a circle to the woman’s left side.

Internal rotation of the shoulders

The shoulders enter the pelvis in the left oblique diameter of the maternal pelvis and the anterior shoulder reaches the pelvic floor first, rotating forwards 1/8 of a circle along the right side of the pelvis.

External rotation of the head

This occurs simultaneously. The chin moves a further 1/8 of a circle to the left.

Lateral flexion

The anterior shoulder escapes under the symphysis pubis, the posterior shoulder sweeps the perineum and the baby’s body is born by a movement of lateral flexion.

Possible course and outcomes of labour

Prolonged labour

Labour is often prolonged because the face is an ill-fitting presenting part and does not therefore stimulate effective uterine contractions. The woman should be kept informed of her progress and any proposed intervention throughout labour.

In addition, the facial bones do not mould and, in order to enable the mentum to reach the pelvic floor and rotate forwards, the shoulders must enter the pelvic cavity at the same time as the head. The fetal axis pressure is directed to the chin and the head is extended almost at right-angles to the spine, increasing the diameters to be accommodated in the pelvis.

Mentoanterior positions

With good uterine contractions, descent and rotation of the head occur and labour progresses to as pontaneous birth as described below.

Mentoposterior positions

If the head is completely extended, so that the mentum reaches the pelvic floor first, and the contractions are effective, the mentum will rotate forwards and the position becomes anterior.

Persistent mentoposterior position

In this case, the head is incompletely extended and the sinciput reaches the pelvic floor first and rotates forwards 1/8 of a circle, which brings the chin into the hollow of the sacrum. There is no further mechanism. The face becomes impacted because, in order to descend further, both head and chest would have to be accommodated in the pelvis. Whatever emerges anteriorly from the vagina must pivot around the subpubic arch. When the chin is posterior this is impossible because the head can extend no further.

Reversal of face presentation

A face presentation in a persistent mentoposterior position may, in some cases, be manipulated to an occipito anterior position using bimanual pressure. This method was developed to reduce the likelihood of an operative birth for those women who refused caesarean section. Using a tocolytic drug, such as terbutaline, to relax the uterus, the fetal head is disengaged using upward transvaginal pressure. The fetal head is then flexed with bimanual pressure under ultrasound guidance to achieve an occipitoanterior position.

Management of labour

First stage of labour

Upon diagnosis of a face presentation, the midwife should inform the doctor of this deviation from the normal. Routine observations of maternal and fetal conditions are made as in a normal physiological labour. A fetal scalp electrode must not be applied, and care should be taken not to infect or injure the eyes during vaginal examinations.

Immediately following rupture of the membranes, a vaginal examination should be performed to exclude cord prolapse which is more likely because the face is an illfitting presenting part. Descent of the fetal head should be assessed abdominally, and careful vaginal examination performed every 2–4 hours to determine cervical dilatation and descent of the head.

In mentoposterior positions the midwife should note whether the mentum is lower than the sinciput, since rotation and descent depend on this. If the head remains high in spite of good contractions, caesarean section is likely.

The woman may be prescribed oral ranitidine, 150 mg every 6 hours throughout labour if it is considered that an anaesthetic may be necessary.

Birth of the head 

When the face appears at the vulva, extension must be maintained by holding back the sinciput and permitting the mentum to escape under the symphysis pubis before the occiput is allowed to sweep the perineum. In this way, the submentovertical diameter (11.5 cm) instead of the mentovertical diameter (13.5 cm) distends the vaginal orifice. Because the perineum is also distended by the biparietal diameter (9.5 cm), an elective episiotomy may be performed to avoid extensive perineal lacerations. If the head does not descend in the second stage of labour, the doctor should be informed. In a mentoanterior position it may be possible for the obstetrician to assist the baby’s birth with forceps when rotation is incomplete. If the position remains mentoposterior, the head has become impacted, or there is any suspicion of disproportion, a caesarean section will be necessary.

Fetal Circulation Physiology and Features

Complications

Obstructed labour

Because the face, unlike the vertex, does not mould, a minor degree of pelvic contraction may result in obstructed labour. In a persistent mentoposterior position the face becomes impacted and caesarean section is necessary.

Cord prolapse

A prolapsed cord is more common when the membranes rupture because the face is an ill-fitting presenting part.

The midwife should always perform a vaginal examination when the membranes rupture to rule out cord prolapse.

Facial bruising

The baby’s face is always bruised and swollen at birth, with oedematous eyelids and lips. The head is elongated and the baby will initially lie with the head extended. The midwife should warn the parents in advance of the baby’s battered appearance, reassuring them that this is only temporary as oedema will disappear within 1or 2 days, with the bruising usually resolving within a week. Trauma during labour may cause tracheal and laryngeal oedema immediately after the birth, which can result in neonatal respiratory distress. In addition, fetal anomalies or tumours, such as fetal goiters that may have contributed to fetal malpresentation, may make intubation difficult. As a result, a clinician with expertise in neonatal resuscitation should be present at the birth.

Cerebral haemorrhage

The lack of moulding of the facial bones can lead to intra cranial haemorrhage caused by excessive compression of the fetal skull or by rearward compression, in the typical moulding of the fetal skull found in this presentation.

Maternal trauma

Extensive perineal lacerations may occur at birth owing to the large submentovertical and biparietal diameters distending the vagina and perineum. There is an increased incidence of operative birth by either forceps or by caesarean section, both of which increase maternal morbidity.