Malpresentations and Malpositions

Usually the fetal head engages in the occipito-anterior position (more often left OA rather than right) and then undergoes a short rotation to be directly occipito-anterior in the mid-cavity. Malpositions are abnormal positions of the vertex of the fetal head relative to the maternal pelvis. Malpresentations are all presentations of the fetus other than vertex.

Predisposing factors to malpresentation include:

• Prematurity
• Multiple pregnancy
• Abnormalities of the uterus, e.g. fibroids
• Partial septate uterus
• Abnormal fetus
• Placenta praevia

Breech presentation

A more detailed discussion of Breech Presentation is discussed in a separate article.

• Breech presentation is the commonest malpresentation, with the majority discovered before labour. Breech presentation is much more common in premature labour.
• Approximately one third are diagnosed during labour when fetus can be directly palpated through the cervix.
• If pelvis is normal and estimated fetal weight is 2500-4000g, assisted breech delivery with experienced staff is believed to be as safe as caesarean section;¹ approximately 50% women aiming for vaginal delivery will achieve this.
• Women who have an elective caesarean section for a breech presentation in their first pregnancy have approx. 1 in 10 chance of having an elective caesarean section for a breech presentation in their second pregnancy.²

Transverse lie

• When fetus positioned with head on one side of the pelvis and buttocks in the other (transverse lie), vaginal delivery is impossible.
• Requires caesarean section unless converts or is converted late in pregnancy. Surgeon may be able to rotate the fetus through the wall of the uterus once abdominal wall has been opened. Otherwise, needs a transverse uterine incision to gain access to a fetal pole.
• Internal podalic version is no longer attempted.

Occipito-posterior position

• Commonest malposition where head initially engages normally but then the occiput rotates posteriorly rather than anteriorly. Approximately 10% of labours begin this way, but many correct in labour.
• The occipito-posterior (OP) position results from a poorly flexed vertex. The anterior fontanelle (four radiating sutures) is felt anteriorly. The posterior fontanelle (three radiating sutures) may also be palpable posteriorly.
• May occur because of flat sacrum, poorly flexed head or weak uterine contractions may not push the head down into the pelvis with sufficient strength to produce correct rotation.
• Occasionally, epidural analgesia relaxes the pelvic floor such that the occiput sinks into it instead of being pushed to the correct position.³

Management

• Often results in a long labour. Close maternal and fetal monitoring is required. An epidural is often recommended and ensure adequate fluids are given to the mother.
• Mother may get the urge to push before full dilatation but this must be discouraged. If head comes into a face to pubis position then vaginal delivery is possible as long as there is a reasonable pelvic size. Otherwise forceps or caesarean section may be required.

Occipito-transverse position

• Head initially engages correctly but fails to rotate and remains in transverse position.
• Alternatives for delivery include:
  • If the second stage is reached the head must be manually rotated with Kielland's forceps or delivered using vacuum extraction. This is inappropriate if there is any fetal acidosis because of the risk of cerebral haemorrhage.
  • Therefore there must be immediate provision for a failure of forceps delivery to be changed immediately to a caesarean. The trial of forceps is therefore often performed in theatre.
  • Some centres prefer to manage by caesarean section without trial of forceps.

Face presentations

• Face presents for delivery if there is complete extension of the fetal head.
• face presentation occurs in 1 in 300 deliveries.
• With adequate pelvis and rotation of the head to the mento-anterior position, should achieve vaginal delivery after a long labour.
• Backwards rotation of the head to a mento-posterior position requires a caesarean section.

Brow positions

• The fetal head stays between full extension and full flexion so that the biggest diameter (the mento-vertex) presents.
• Brow presentation occurs in 1 in 500 deliveries.
• Brow presentation is usually only diagnosed once labour is well established.
• The anterior fontanelle and super orbital ridges are palpable on vaginal examination.
• Unless the head flexes, a vaginal delivery is not possible, and a caesarean section is required.