Face and Brow Presentation
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At the onset of labor, assessment of the fetal presentation with respect to the maternal birth canal is critical to the route of delivery. At term, the vast majority of fetuses present in the vertex presentation, where the fetal head is flexed so that the chin is in contact with the fetal thorax. The fetal spine typically lies along the longitudinal axis of the uterus. Nonvertex presentations (including breech, transverse lie, face, brow, and compound presentations) occur in less than 4% of fetuses at term. Malpresentation of the vertex presentation occurs if there is deflexion or extension of the fetal head leading to brow or face presentation, respectively.
In a face presentation, the fetal head and neck are hyperextended, causing the occiput to come in contact with the upper back of the fetus while lying in a longitudinal axis. The presenting portion of the fetus is the fetal face between the orbital ridges and the chin. The fetal chin (mentum) is the point designated for reference during an internal examination through the cervix. The occiput of a vertex is usually hard and has a smooth contour, while the face and brow tend to be more irregular and soft. Like the occiput, the mentum can present in any position relative to the maternal pelvis. For example, if the mentum presents in the left anterior quadrant of the maternal pelvis, it is designated as left mentum anterior (LMA).
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. The face and chin are not included. 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).
Face presentation occurs in 1 of every 600-800 live births, averaging about 0.2% of live births. Causative factors associated with a face presentation are similar to those leading to general malpresentation and those that prevent head flexion or favor extension. Possible etiology includes multiple gestations, grand multiparity, fetal malformations, prematurity, and cephalopelvic disproportion. At least one etiological factor may be identified in up to 90% of cases with face presentation.
Fetal anomalies such as hydrocephalus, anencephaly, and neck masses are common risk factors and may account for as many as 60% of cases of face presentation. For example, anencephaly is found in more than 30% of cases of face presentation. Fetal thyromegaly and neck masses also lead to extension of the fetal head.
A contracted pelvis or cephalopelvic disproportion, from either a small pelvis or a large fetus, occurs in 10-40% of cases. Multiparity or a large abdomen can cause decreased uterine tone, leading to natural extension of the fetal head.
Face presentation is diagnosed late in the first or second stage of labor by examination of a dilated cervix. On digital examination, the distinctive facial features of the nose, mouth, and chin, the malar bones, and particularly the orbital ridges can be palpated. This presentation can be confused with a breech presentation because the mouth may be confused with the anus and the malar bones or orbital ridges may be confused with the ischial tuberosities. The facial presentation has a triangular configuration of the mouth to the orbital ridges compared to the breech presentation of the anus and fetal genitalia. During Leopold maneuvers, diagnosis is very unlikely. Diagnosis can be confirmed by ultrasound evaluation, which reveals a hyperextended fetal neck.
Brow presentation is the least common of all fetal presentations and the incidence varies from 1 in 500 deliveries to 1 in 1400 deliveries. Brow presentation may be encountered early in labor but is usually a transitional state and converts to a vertex presentation after the fetal neck flexes. Occasionally, further extension may occur resulting in a face presentation.
The causes of a persistent brow presentation are generally similar to those causing a face presentation and include cephalopelvic disproportion or pelvic contracture, increasing parity and prematurity. These are implicated in more than 60% of cases of persistent brow presentation. Premature rupture of membranes may precede brow presentation in as many as 27% of cases.
Diagnosis of a brow presentation can occasionally be made with abdominal palpation by 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 examination of a dilated cervix. The orbital ridge, eyes, nose, forehead, and anterior fontanelle are palpated. The mouth and chin are not palpable, thus excluding face presentation. Fetal ultrasound evaluation again notes a hyperextended neck.
As with 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 mentum anterior, which occurs about twice as often as either transverse or posterior positions. A higher cesarean delivery rate occurs with a mentum transverse or posterior [1] position than with a mentum anterior position.
The mechanism of labor consists of the cardinal movements of engagement, descent, flexion, internal rotation, and the accessory movements of extension and external rotation. Intuitively, the cardinal movements of labor for a face presentation are not completely identical to those of a vertex presentation.
While descending into the pelvis, the natural contractile forces combined with the maternal pelvic architecture allow the fetal head to either flex or extend. In the vertex presentation, the vertex is flexed such that the chin rests on the fetal chest, allowing the suboccipitobregmatic diameter of approximately 9.5 cm to be the widest diameter through the maternal pelvis. This is the smallest of the diameters to negotiate the maternal pelvis. Following engagement in the face presentation, descent is made. The widest diameter of the fetal head negotiating the pelvis is the trachelobregmatic or submentobregmatic diameter, which is 10.2 cm (0.7 cm larger than the suboccipitobregmatic diameter). Because of this increased diameter, engagement does not occur until the face is at +2 station.
Fetuses with face presentation may initially begin labor in the brow position. Using x-ray pelvimetry in a series of 7 patients, Borrell and Ferstrom demonstrated that internal rotation occurs between the ischial spines and the ischial tuberosities, making the chin the presenting part, lower than in the vertex presentation. [2, 3] Following internal rotation, the mentum is below the maternal symphysis, and delivery occurs by flexion of the fetal neck. As the face descends onto the perineum, the anterior fetal chin passes under the symphysis and flexion of the head occurs, making delivery possible with maternal expulsive forces.
The above mechanisms of labor in the term infant can occur only if the mentum is anterior and at term, only the mentum anterior face presentation is likely to deliver vaginally. If the mentum is posterior or transverse, the fetal neck is too short to span the length of the maternal sacrum and is already at the point of maximal extension. The head cannot deliver as it cannot extend any further through the symphysis and cesarean delivery is the safest route of delivery.
Fortunately, the mentum is anterior in over 60% of cases of face presentation, transverse in 10-12% of cases, and posterior only 20-25% of the time. Fetuses with the mentum transverse position usually rotate to the mentum anterior position, and 25-33% of fetuses with mentum posterior position rotate to a mentum anterior position. When the mentum is posterior, the neck, head and shoulders must enter the pelvis simultaneously, resulting in a diameter too large for the maternal pelvis to accommodate unless in the very preterm or small infant.
Three labor courses are possible when the fetal head engages in a brow presentation. The brow may convert to a vertex presentation, to a face presentation, or remain as a persistent brow presentation. More than 50% of brow presentations will convert to vertex or face presentation and 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. Descent and internal rotation occur only with an adequate pelvis and if the face can fit under the pubic arch. While the head descends, it becomes wedged into the hollow of the sacrum. Downward pressure from uterine contractions and maternal expulsive forces may cause the mentum to extend anteriorly and low to present at the perineum as a mentum anterior face presentation.
If internal rotation does not occur, the occipitomental diameter, which measures 1.5 cm wider than the suboccipitobregmatic diameter and is thus the largest diameter of the fetal head, presents at the pelvic inlet. The head may engage 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. This may result in a missed diagnosis in a patient who presents later in active labor.
If the mentum is anterior and the forces of labor are directed toward the fetal occiput, flexing the head and pivoting the face under the pubic arch, there is conversion to a vertex 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.
The persistent brow presentation with subsequent delivery only occurs in cases of a large pelvis and/or a small infant. Women with gynecoid pelvis or multiparity may be given the option to labor; however, dysfunctional labor and cephalopelvic disproportion are more likely if this presentation persists.
Labor management of face and brow presentation requires close observation of labor progression because cephalopelvic disproportion, dysfunctional labor, and prolonged labor are much more common. As mentioned above, the trachelobregmatic or submentobregmatic diameters are larger than the suboccipitobregmatic diameter. Duration of labor with a face presentation is generally the same as duration of labor with a vertex presentation, although a prolonged labor may occur. As long as maternal or fetal compromise is not evident, labor with a face presentation may continue. [4] A persistent mentum posterior presentation is an indication for delivery by cesarean section.
Continuous electronic fetal heart rate monitoring is considered mandatory by many authors because of the increased incidence of abnormal fetal heart rate patterns and/or nonreassuring fetal heart rate patterns. [5] An internal fetal scalp electrode may be used, but very careful application of the electrode must be ensured. The mentum is the recommended site of application. Facial edema is common and can obscure the fetal facial anatomy and improper placement can lead to facial and ophthalmic injuries. Oxytocin can be used to augment labor using the same precautions as in a vertex presentation and the same criteria of assessment of uterine activity, adequacy of the pelvis, and reassuring fetal heart tracing.
Fetuses with face presentation can be delivered vaginally with overall success rates of 60-70%, while more than 20% of fetuses with face presentation require cesarean delivery. Cesarean delivery is performed for the usual obstetrical indications, including arrest of labor and nonreassuring fetal heart rate pattern.
Attempts to manually convert the face to vertex (Thom maneuver) or to rotate a posterior position to a more favorable anterior mentum position are rarely successful and are associated with high fetal morbidity and mortality and maternal morbidity, including cord prolapse, uterine rupture, and fetal cervical spine injury with neurological impairment. Given the availability and safety of cesarean delivery, internal rotation maneuvers are no longer justified unless cesarean section cannot be readily performed.
Internal podalic version and breech extraction are also no longer recommended in the modern management of the face presentation. [6]
Operative delivery with forceps must be approached with caution. Since engagement occurs when the face is at +2 position, forceps should only be applied to the face that has caused the perineum to bulge. Increased complications to both mother and fetus can occur [7] and operative delivery must be approached with caution or reserved when cesarean section is not readily available. Forceps may be used if the mentum is anterior. Although the landmarks are different, the application of any forceps is made as if the fetus were presenting directly in the occiput anterior position. The mouth substitutes for the posterior fontanelle, and the mentum substitutes for the occiput. Traction should be downward to maintain extension until the mentum passes under the symphysis, and then gradually elevated to allow the head to deliver by flexion. During delivery, hyperextension of the fetal head should be avoided.
As previously mentioned, the persistent brow presentation has a poor prognosis for vaginal delivery unless the fetus is small, premature, or the maternal pelvis is large. Expectant management is reasonable if labor is progressing well and the fetal well-being is assessed, as there can be spontaneous conversion to face or vertex presentation. The earlier in labor that brow presentation is diagnosed, the higher the likelihood of conversion. Minimal intervention during labor is recommended and some feel the use of oxytocin in the brow presentation is contraindicated.
The use of operative vaginal delivery or manual conversion of a brow to a more favorable presentation is contraindicated as the risks of perinatal morbidity and mortality are unacceptably high. Prolonged, dysfunctional, and arrest of labor are common, necessitating cesarean section delivery.
The incidence of perinatal morbidity and mortality and maternal morbidity has decreased due to the increased incidence of cesarean section delivery for malpresentation, including face and brow presentation.
Neonates delivered in the face presentation exhibit significant facial and skull edema, which usually resolves within 24-48 hours. Trauma during labor may cause tracheal and laryngeal edema immediately after delivery, which can result in neonatal respiratory distress. In addition, fetal anomalies or tumors, such as fetal goiters that may have contributed to fetal malpresentation, may make intubation difficult. Physicians with expertise in neonatal resuscitation should be present at delivery in the event that intubation is required. When a fetal anomaly has been previously diagnosed by ultrasonographic evaluation, the appropriate pediatric specialists should be consulted and informed at time of labor.
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Teresa Marino, MD Assistant Professor, Attending Physician, Division of Maternal-Fetal Medicine, Tufts Medical Center
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Carl V Smith, MD The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, Senior Associate Dean for Clinical Affairs, University of Nebraska Medical Center
Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Society for Maternal-Fetal Medicine, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association
Disclosure: Nothing to disclose.
Chitra M Iyer, MD, Perinatologist, Obstetrix Medical Group, Fort Worth, Texas.
Chitra M Iyer, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Society of Maternal-Fetal Medicine.
Disclosure: Nothing to disclose.
Face and Brow Presentation
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