Delivery, Face and Brow Presentation

Anatomy and Physiology

Before discussing the mechanism of labor in the face or brow presentation, it is crucial to highlight some anatomical landmarks and their measurements. 

Planes and Diameters of the Pelvis

The three most important planes in the female pelvis are the pelvic inlet, mid pelvis, and pelvic outlet. 

Four diameters can describe the pelvic inlet: anteroposterior, transverse, and two obliques. Furthermore, based on the different landmarks on the pelvic inlet, there are three different anteroposterior diameters, named conjugates: true conjugate, obstetrical conjugate, and diagonal conjugate. Only the latter can be measured directly during the obstetric examination. The shortest of these three diameters is obstetrical conjugate, which measures approximately 10.5 cm and is a distance between the sacral promontory and 1 cm below the upper border of the symphysis pubis. This measurement is clinically significant as the fetal head must pass through this diameter during the engagement phase. The transverse diameter measures about 13.5cm and is the widest distance between the innominate line on both sides. 

The shortest distance in the mid pelvis is the interspinous diameter and usually is only about 10 cm. 

Fetal Skull Diameters

There are six distinguished longitudinal fetal skull diameters:

1. Suboccipito-bregmatic: from the center of anterior fontanelle (bregma) to the occipital protuberance, measuring 9.5 cm. This is the presenting diameter in vertex presentation. 
2. Suboccipito-frontal: from the anterior part of bregma to the occipital protuberance, measuring 10 cm 
3. Occipito-frontal: from the root of the nose to the most prominent part of the occiput, measuring 11.5cm
4. Submento-bregmatic: from the center of the bregma to the angle of the mandible, measuring 9.5 cm. This is the presenting diameter in face presentation where the neck is hyperextended. 
5. Submento-vertical: from the midpoint between fontanelles and the angle of the mandible, measuring 11.5cm 
6. Occipito-mental: from the midpoint between fontanelles and the tip of the chin, measuring 13.5 cm. It is the presenting diameter in brow presentation. 

Cardinal Movements of Normal Labor

1. Engagement
2. Decent
3. Neck flexion
4. Internal rotation
5. Extension (delivers head)
6. External rotation (Restitution)
7. Expulsion (delivery of anterior and posterior shoulders)

Some of the key movements are not possible in the face or brow presentations.  

Based on the information provided above, it is obvious that labor will be arrested in brow presentation unless it spontaneously changes to face or vertex, as the occipito-mental diameter of the fetal head is significantly wider than the smallest diameter of the female pelvis. Face presentation can, however, be delivered vaginally, and further mechanisms of face delivery will be explained in later sections.

Indications

As mentioned previously, spontaneous vaginal delivery can be successful in face presentation. However, the main indication for vaginal delivery in such circumstances would be a maternal choice. It is crucial to have a thorough conversation with a mother, explaining the risks and benefits of vaginal delivery with face presentation and a cesarean section. Informed consent and creating a rapport with the mother is an essential aspect of safe and successful labor.

Contraindications

Vaginal delivery of face presentation is contraindicated if the mentum is lying posteriorly or is in a transverse position. In such a scenario, the fetal brow is pressing against the maternal symphysis pubis, and the short fetal neck, which is already maximally extended, cannot span the surface of the maternal sacrum. In this position, the diameter of the head is larger than the maternal pelvis, and it cannot descend through the birth canal. Therefore the cesarean section is recommended as the safest mode of delivery for mentum posterior face presentations. 

Attempts to manually convert face presentation to vertex, manual or forceps rotation of the persistent posterior chin to anterior are contraindicated as they can be dangerous.

Persistent brow presentation itself is a contraindication for vaginal delivery unless the fetus is significantly small or the maternal pelvis is large.

Equipment

Continuous electronic fetal heart rate monitoring is recommended for face and brow presentations, as heart rate abnormalities are common in these scenarios. One study found that only 14% of the cases with face presentation had no abnormal traces on the cardiotocograph.[8] It is advised to use external transducer devices to prevent damage to the eyes. When internal monitoring is inevitable, it is suggested to place monitoring devices on bony parts carefully. 

Personnel

People who are usually involved in the delivery of face/ brow presentation are:

• Experienced midwife, preferably looking after laboring woman 1:1
• Senior obstetrician 
• Neonatal team - in case of need for resuscitation 
• Anesthetic team - to provide necessary pain control (e.g., epidural)
• Theatre team  - in case of failure to progress and an emergency cesarean section will be required.

Preparation

No specific preparation is required for face or brow presentation. However, it is essential to discuss the labor options with the mother and birthing partner and inform members of the neonatal, anesthetic, and theatre co-ordinating teams.

Technique or Treatment

Mechanism of Labor in Face Presentation

During contractions, the pressure exerted by the fundus of the uterus on the fetus and pressure of amniotic fluid initiate descent. During this descent, the fetal neck extends instead of flexing. The internal rotation determines the outcome of delivery, if the fetal chin rotates posteriorly, vaginal delivery would not be possible, and cesarean section is permitted. The approach towards mentum-posterior delivery should be individualized, as the cases are rare. Expectant management is acceptable in multiparous women with small fetuses, as a spontaneous mentum-anterior rotation can occur. However, there should be a low threshold for cesarean section in primigravida women or women with large fetuses.

When the fetal chin is rotated towards maternal symphysis pubis as described as mentum-anterior; in these cases further descend through the vaginal canal continues with approximately 73% cases deliver spontaneously.[9] Fetal mentum presses on the maternal symphysis pubis, and the head is delivered by flexion. The occiput is pointing towards the maternal back, and external rotation happens. Shoulders are delivered in the same manner as in vertex delivery.

Mechanism of Labor in Brow Presentation

As this presentation is considered unstable, it is usually converted into a face or an occiput presentation. Due to the cephalic diameter being wider than the maternal pelvis, the fetal head cannot engage; thus, brow delivery cannot take place. Unless the fetus is small or the pelvis is very wide, the prognosis for vaginal delivery is poor. With persistent brow presentation, a cesarean section is required for safe delivery.

Complications

As the cesarean section is becoming a more accessible mode of delivery in malpresentations, the incidence of maternal and fetal morbidity and mortality during face presentation has dropped significantly.[10]

However, there are still some complications associated with the nature of labor in face presentation. Due to the fetal head position, it is more challenging for the head to engage in the birth canal and descend, resulting in prolonged labor.

Prolonged labor itself can provoke foetal distress and arrhythmias. If the labor arrests or signs of fetal distress appear on CTG, the recommended next step in management is an emergency cesarean section, which in itself carries a myriad of operative and post-operative complications.

Finally, due to the nature of the fetal position and prolonged duration of labor in face presentation, neonates develop significant edema of the skull and face. Swelling of the fetal airway may also be present, resulting in respiratory distress after birth and possible intubation.

Clinical Significance

During vertex presentation, the fetal head flexes, bringing the chin to the chest, forming the smallest possible fetal head diameter, measuring approximately 9.5cm. With face and brow presentation, the neck hyperextends, resulting in greater cephalic diameters. As a result, the fetal head will engage later, and labor will progress more slowly. Failure to progress in labor is also more common in both presentations compared to vertex presentation.

Furthermore, when the fetal chin is in a posterior position, this prevents further flexion of the fetal neck, as browns are pressing on the symphysis pubis. As a result, descend through the birth canal is impossible. Such presentation is considered undeliverable vaginally and requires an emergency cesarean section.

Manual attempts to change face presentation to vertex, manual or forceps rotation to mentum anterior are considered dangerous and are discouraged.

Enhancing Healthcare Team Outcomes

A multidisciplinary team of healthcare experts supports the woman and her child during labor and the perinatal period. For a face or brow presentation to be appropriately diagnosed, an experienced midwife and obstetrician must be involved in the vaginal examination and labor monitoring. As fetal anomalies, such as anencephaly or goiter, can contribute to face presentation, sonographers experienced in antenatal scanning should also be involved in the care. It is advised to inform the anesthetic and neonatal teams in advance of the possible need for emergency cesarean section and resuscitation of the neonate.[11][12]