Dystocia with the fetal head as the presenting part, also referred to as cephalic dystocia, is the most common type of fetal malposition.

Persistent Occiput Posterior Position and Occiput Transverse Position

When the fetal head engages in the maternal pelvis in the occiput posterior or occiput transverse position, internal rotation occurs as the biparietal diameter of the fetal head reaches the mid-pelvic plane. In most cases, the fetal head rotates anteriorly into an occiput anterior position, allowing the smallest diameter of the head to pass through the narrowest plane of the pelvis, facilitating natural vaginal delivery. However, in cases where after adequate trial labor the occiput fails to rotate anteriorly and remains positioned posteriorly or laterally in the maternal pelvis, this results in labor difficulties, a condition known as persistent occiput posterior position or persistent occiput transverse position. This condition accounts for approximately 5% of all deliveries.

Causes

Abnormal Pelvis and Poor Fetal Head Flexion

These are commonly seen in android pelvis types and anthropoid pelvises, which have a narrower anterior portion and a wider posterior portion of the inlet plane, allowing engagement in the occiput posterior or occiput transverse position.

Both types are frequently associated with mid-pelvic narrowing, which impedes internal rotation of the fetal head, increasing the chances of persistent occiput posterior or transverse positions.

A flat pelvis or a uniformly reduced pelvis facilitates engagement with the occiput transverse position, particularly when poor fetal head flexion and difficulties with internal rotation occur, resulting in the fetal head becoming arrested at the mid-pelvis and leading to a persistent occiput transverse position.

Other Abnormalities

Factors such as cervical myomas, cephalopelvic disproportion, placenta previa, uterine hypotonia, oversized or undersized fetuses, and fetal developmental abnormalities may all disrupt fetal head flexion and internal rotation, resulting in persistent occiput posterior or transverse positions.

Diagnosis

Clinical Manifestations

Engagement in the occiput posterior position leads to poor fetal head flexion and slow descent of the fetal head after the onset of labor, preventing effective cervical dilation. Reflexive stimulation of endogenous oxytocin release may cause uterine contractions to become uncoordinated, prolonging the second stage of labor.

In nulliparous women, labor duration increases by an average of 2 hours, while in multiparous women, the increase is around 1 hour.

Compression of the maternal rectum by the fetal occiput may cause a sensation of rectal pressure and a false urge to defecate before full cervical dilation. Premature bearing down may lead to excessive maternal exhaustion, cervical anterior lip edema, and slowed or arrested descent of the fetal head, further prolonging labor.

Abdominal Examination

Fetal limbs may be easily palpable along the maternal anterior abdominal wall, with the fetal back deviated toward the maternal posterior or lateral side. Fetal heart sounds are usually heard on the same side as the fetal limbs.

Vaginal and Rectal Examination

In occiput posterior positions, the posterior pelvis may feel empty. The sagittal suture of the fetal head aligns with the transverse diameter of the maternal pelvis.

If the posterior fontanelle is on the left side, it indicates the left occiput transverse position; if on the right, it indicates the right occiput transverse position.

If the sagittal suture lies along the left oblique diameter of the pelvis with the anterior fontanelle in the right anterior pelvis and the posterior fontanelle in the left posterior pelvis, it indicates the left occiput posterior position; the reverse indicates the right occiput posterior position.

Figure 1 Persistent occiput posterior and occiput transverse positions

Poor flexion of the fetal head is suggested when the anterior fontanelle lies lower than the posterior fontanelle.

When complete cervical dilation occurs, the cephalic sutures and fontanelles may be difficult to palpate due to fetal head edema and overlapping cranial bones. In such cases, the position of the auricle and tragus can be used to determine fetal orientation.

Rectal examination can also be performed to assess the posterior pelvis and confirm fetal orientation. Sterile paper should cover the vaginal opening to prevent fecal contamination, and the examiner should insert a lubricated gloved index finger into the rectum for assessment.

Ultrasound Examination

Ultrasound can clearly identify the position of the fetal occiput and orbits to ascertain the fetal head orientation.

Mechanisms of Delivery

In the absence of cephalopelvic disproportion, the majority of occiput posterior and transverse positions can resolve with strong uterine contractions, allowing the occiput to rotate anteriorly by 90°–135° to become occiput anterior. If spontaneous rotation to the occiput anterior position does not occur during labor, the following delivery mechanisms may be encountered:

Occiput Posterior Position

During internal rotation, the left or right occiput posterior position may rotate posteriorly by 45° to become the direct occiput posterior position. This condition may lead to two outcomes:

Good Flexion

The fetal head descends until the anterior fontanelle reaches the subpubic arch. The anterior fontanelle becomes the pivot point, allowing the head to flex further, delivering the vertex and occiput beyond the perineum. This is followed by extension of the fetal head to deliver the brow, nose, mouth, and chin sequentially under the subpubic arch. This is the most common mechanism of vaginal assisted delivery for occiput posterior positions.

Poor Flexion

The fetal head rotates with a larger occipitofrontal circumference, making delivery more challenging. Aside from rare instances of strong maternal forces and small fetuses achieving spontaneous delivery, operative assistance is typically required. The forehead may present first, and as the nasal root reaches the subpubic arch, it becomes the pivot point. The head then flexes to deliver the anterior fontanelle, vertex, and occiput, followed by extension to deliver the brow, nose, mouth, and chin sequentially.

Figure 2 Mechanism of delivery in occiput posterior position

Occiput Transverse Position

Delivery is generally possible through the vaginal route but often requires assistance, either manual or with vacuum extraction (or forceps), to rotate the head into the occiput anterior position for delivery. If internal rotation is obstructed or the occiput posterior position rotates forward by only 45°, yielding a persistent occiput transverse position, caution must be exercised.

Impact on Labor, Mother, and Fetus

Impact on Labor Progression

Persistent occiput posterior (or transverse) position often leads to delayed descent or even arrest of the fetal head during the second stage of labor. If not addressed in a timely manner, it can result in prolonged second-stage labor.

Impact on the Mother

This condition frequently causes secondary uterine hypotonia and subsequently prolongs labor. Prolonged fetal head compression on the soft birth canal may result in ischemia, necrosis, or tissue sloughing. Compression of adjacent organs, such as bladder paralysis, can lead to urinary retention and, in severe cases, genital tract injuries or fistula formation. Vaginal assisted deliveries become more common in these cases, increasing the risk of soft birth canal tears, postpartum hemorrhage, and puerperal infections.

Impact on the Fetus

Prolonged second-stage labor and the increased likelihood of operative delivery raise the risk of fetal distress and neonatal asphyxia, leading to a higher perinatal mortality rate.

Management

In cases of persistent occiput posterior or transverse position without pelvic abnormalities or a large fetus, trial labor may be allowed with close monitoring of labor progression, including uterine contraction strength, cervical dilation, fetal head descent, and any changes in fetal heart rate.

First Stage of Labor

Latent Phase

Adequate rest and nutrition for the mother are essential. Administration of pethidine is possible. In cases of uterine hypotonia, oxytocin may be used.

Active Phase

Mothers should avoid bearing down prematurely before full cervical dilation. After ruling out cephalopelvic disproportion, artificial rupture of membranes can be performed when the cervical dilation exceeds 3–5 cm, followed by a vaginal examination to assess pelvic size. Oxytocin infusion may be administered to augment uterine contractions, enabling vaginal delivery if conditions allow. If signs of fetal distress develop during trial labor or if artificial rupture of membranes and oxytocin infusion fail to produce effective progress, defined as cervical dilation increasing by less than 0.5 cm per hour or no progress at all, cesarean delivery should be performed to complete labor.

Second Stage of Labor

If labor progress in the second stage is slow—defined as nearing 2 hours in nulliparous women or 1 hour in multiparous women—a vaginal examination should be conducted to determine fetal position.

If the station is S+3 or lower (biparietal diameter at or below the ischial spines), manual rotation of the occiput to the anterior position can be attempted. Alternatively, vacuum extraction or forceps may be used to assist fetal head rotation into the occiput anterior position and facilitate vaginal delivery.

If manual rotation to the anterior position proves difficult, rotation to the direct occiput posterior position may be attempted to enable assisted delivery using forceps. If the fetus is delivered in the occiput posterior position, the poor flexion of the fetal head often results in delivery along the occipitofrontal diameter. To prevent perineal tears, a more extensive mediolateral episiotomy may be performed to assist delivery.

If labor in the second stage is prolonged and the fetal biparietal diameter remains above the ischial spines (above S+2) or if accompanied by fetal distress, cesarean delivery should be considered.

Figure 3 Manual internal rotation of the fetal head

Third Stage of Labor

Preparation for neonatal resuscitation is necessary. Given the increased risk of uterine hypotonia due to prolonged labor, uterotonic agents should be administered immediately after placental delivery to prevent postpartum hemorrhage. If soft birth canal lacerations are present, timely repair should be performed, along with administration of antibiotics to prevent infection.

Persistent Occipitoanterior and Occipitoposterior Positions of the Fetal Head (Sincipital Presentation)

When the fetal head engages in the pelvis in a neutral attitude, neither flexed nor extended, along the occipitofrontal diameter, and the sagittal suture aligns with the anteroposterior diameter of the pelvic inlet, this presentation is referred to as a persistent occipitoanterior or occipitoposterior position, collectively known as sincipital presentation. These include:

Persistent occipitoanterior position: the occiput of the fetal head is oriented anteriorly toward the pubic symphysis; also referred to as the occipitopubic position.
Persistent occipitoposterior position: the occiput is directed posteriorly toward the sacral promontory; also called the occipitosacral position.

These presentations account for approximately 1% of all deliveries. They pose significant risks to both mother and fetus and require appropriate management.