eMedicine Specialties > Obstetrics and Gynecology > Labor and Delivery
Brow Presentation
Updated: Jan 11, 2008
Introduction
In a brow presentation, the fetal head is midway between full flexion (vertex) and hyperextension (face) along a longitudinal axis. The presenting portion of the fetal head is between the orbital ridge, and the anterior fontanel presents at the pelvic inlet. The frontal bones are the point of designation and can present (as with the occiput during a vertex delivery) in any position relative to the maternal pelvis. When the sagittal suture is transverse to the pelvic axis and the anterior fontanel is on the right maternal side, the fetus would be in the right frontotransverse position (RFT).
Background
Brow presentation is the least common of all fetal presentations. Incidence varies from 1 in 500 deliveries to 1 in 3543 deliveries. Early in labor, a brow presentation may be encountered, but this is often unstable, and it converts to a vertex presentation. Occasionally, extension may result in a face presentation. The causes of a persistent brow presentation are generally similar to those causing a face presentation. These include cephalopelvic disproportion or pelvic contracture and increasing parity and prematurity, which are implicated in more than 60% of cases of persistent brow presentation. Premature rupture of membranes preceded brow presentation in as many as 27% of cases.
Diagnosis of a brow presentation by abdominal palpation can be made with Leopold maneuvers. A prominent occipital prominence is encountered along the fetal back, and the fetal chin is also palpable; however, the diagnosis of a brow presentation is usually confirmed by vaginal examination. The orbital ridge, eyes, nose, frontal sutures, and anterior fontanel are palpated. The mouth and chin are not palpable.
As with a face presentation, diagnosis is often made late in labor with half of cases occurring in the second stage of labor. The most common position is the frontum anterior, which occurs about twice as often as either transverse or posterior positions. A higher cesarean delivery rate occurs with a frontum transverse or a frontum posterior position than with a frontum anterior.
Mechanism of Labor
Three labor courses are possible when the fetal head engages in a brow presentation. The brow may convert to a vertex presentation, convert to a face presentation, or remain as a persistent brow presentation. The earlier in labor the diagnosis is made, the more likely conversion is to occur. Vertex or face presentation labor courses are managed accordingly when spontaneous conversion occurs.
In the brow presentation, the occipitomental diameter, which is the largest diameter of the fetal head, is the presenting portion. The head engages but can descend only with significant molding. This molding and subsequent caput succedaneum over the forehead can become so extensive that identification of the brow by palpation is impossible late in labor, which may result in a missed diagnosis in a patient who presents later in active labor.
Descent and internal rotation occur with an adequate pelvis and if the face can fit under the pubic arch. The persistent brow presentation with subsequent delivery only occurs in cases of a large pelvis and/or a small infant. At any time during labor, a brow presentation may convert to a face or vertex presentation.
If the frontum is anterior and the forces of labor are directed toward the fetal occiput, flex the head and pivot the face under the pubic arch, thus converting the fetal head to an occiput-posterior position. If the occiput lies against the sacrum and the forces of labor are directed against the fetal mentum, the neck may extend further, leading to a face presentation.
Labor Management
If the fetus continues with a brow presentation, the prognosis of a vaginal delivery is poor unless the fetus is small and/or the maternal pelvis is large. Expectant management is reasonable as long as the fetal heart tracing remains reassuring and dilation and descent are progressing normally because spontaneous conversion to vertex or face may occur. If dilation or descent ceases or if fetal heart tracing is not reassuring, cesarean delivery is indicated. Minimal intervention is generally best if labor is progressing normally.
Some authors believe that the use of oxytocin in brow presentation is contraindicated because of the increased risk of cephalopelvic disproportion; however, the use of oxytocin to correct an inadequate contraction pattern has been described. Less than half of fetuses with persistent brow presentations undergo spontaneous vaginal delivery, but a trial of labor is not contraindicated in most cases. Prolonged labor and secondary arrest are common in 33-50% of brow presentations. The use of forceps or manual conversion to convert a brow presentation to a more favorable position is contraindicated.
Keywords
vertex presentation, face presentation, Leopold maneuvers, oxytocin augmentation, labor, cesarean delivery, C-section
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References
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Further Reading
Keywords
vertex presentation, face presentation, Leopold maneuvers, oxytocin augmentation, labor, cesarean delivery, C-section
