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B27. Fetal rotational anomalies

Many foetuses enter labour in occiput posterior or occiput transverse position, but then undergo spontaneous rotation to occiput anterior during labour. Abnormalities of the foetal rotation (malrotation) refers to when rotation of the foetal head in the pelvis does not occur correctly during labour, and spontaneous rotation to occiput anterior does not occur. These include persistent occiput posterior and persistent occiput transverse.

Malrotation may prolong or arrest labour in the first or second stage. Their presence increases the risk for maternal and foetal morbidity.

Persistent occiput posterior

Persistent occiput posterior (OP) refers to when the foetus is in an occiput posterior position and does not spontaneously rotate to occiput anterior.

Etiology

Persistent occiput posterior can occur due to a pelvis with a high pubic bone and narrow pubic arch, abnormal skull size, etc. Neuraxial anaesthesia is also a risk factor.

Pathomechanism

Persistent OP may occur for two reasons:

  • A foetus which initially was occiput posterior (OP) before labour never spontaneously rotates to OA
  • A foetus which was occiput anterior (OA) rotates externally to occiput posterior (OP) during labour

Most (50 – 80%) foetuses which are occiput posterior (OP) before labour or during early labour rotate spontaneously to occiput anterior (OA) during the first or early second stage. If spontaneous rotation does not occur by the early second stage, persistent occiput posterior is present.

Diagnosis and evaluation

It is diagnosed on physical examination, which reveals that the anterior fontanelle lies anteriorly. Ultrasound can be used to assist diagnosis.

Management

We may attempt to reposition the mother on the side to achieve foetal rotation. Rotation of the foetus manually (with hands) or with forceps may be attempted. If unsuccessful, operative vaginal delivery or C-section is performed.

Persistent occiput transverse

Persistent occiput transverse (OT), also called persistent transverse position or deep transverse arrest, is the condition when the foetal head is stuck in occiput transverse position during labour. The head remains in the transverse position, which cannot pass the pelvis, causing arrest of labour.

Pathomechanism

Persistent OT may occur for two reasons:

  • A foetus which initially was occiput transverse before labour never spontaneously rotates to OA or OP
  • A foetus which was occiput anterior (OA) rotates internally to occiput transverse (OT) during labour

Like for persistent occiput posterior, most (90 – 95%) foetuses which are occiput transverse (OT) before labour or during early labour rotate spontaneously to occiput anterior (OA) or occiput posterior (OT) during the first or early second stage. If spontaneous rotation does not occur by the early second stage, persistent occiput transverse is present.

Diagnosis and evaluation

It is diagnosed on physical examination, which reveals that the sagittal suture and fontanelles are palpable in the transverse diameter of the pelvis. Ultrasound can be used to assist diagnosis.

Management

We may attempt to reposition the mother on the side to achieve foetal rotation. Rotation of the foetus manually (with hands) or with forceps may be attempted. If unsuccessful, C-section may be necessary (operative vaginal delivery is not possible).