what mean brow presentation

Fetal Presentation, Position, and Lie (Including Breech Presentation)

Variations in Fetal Position and Presentation |

During pregnancy, the fetus can be positioned in many different ways inside the mother's uterus. The fetus may be head up or down or facing the mother's back or front. At first, the fetus can move around easily or shift position as the mother moves. Toward the end of the pregnancy the fetus is larger, has less room to move, and stays in one position. How the fetus is positioned has an important effect on delivery and, for certain positions, a cesarean delivery is necessary. There are medical terms that describe precisely how the fetus is positioned, and identifying the fetal position helps doctors to anticipate potential difficulties during labor and delivery.

Presentation refers to the part of the fetus’s body that leads the way out through the birth canal (called the presenting part). Usually, the head leads the way, but sometimes the buttocks (breech presentation), shoulder, or face leads the way.

Position refers to whether the fetus is facing backward (occiput anterior) or forward (occiput posterior). The occiput is a bone at the back of the baby's head. Therefore, facing backward is called occiput anterior (facing the mother’s back and facing down when the mother lies on her back). Facing forward is called occiput posterior (facing toward the mother's pubic bone and facing up when the mother lies on her back).

Lie refers to the angle of the fetus in relation to the mother and the uterus. Up-and-down (with the baby's spine parallel to mother's spine, called longitudinal) is normal, but sometimes the lie is sideways (transverse) or at an angle (oblique).

For these aspects of fetal positioning, the combination that is the most common, safest, and easiest for the mother to deliver is the following:

Head first (called vertex or cephalic presentation)

Facing backward (occiput anterior position)

Spine parallel to mother's spine (longitudinal lie)

Neck bent forward with chin tucked

Arms folded across the chest

If the fetus is in a different position, lie, or presentation, labor may be more difficult, and a normal vaginal delivery may not be possible.

Variations in fetal presentation, position, or lie may occur when

The fetus is too large for the mother's pelvis (fetopelvic disproportion).

The uterus is abnormally shaped or contains growths such as fibroids .

The fetus has a birth defect .

There is more than one fetus (multiple gestation).

Position and Presentation of the Fetus

Variations in fetal position and presentation.

Some variations in position and presentation that make delivery difficult occur frequently.

Occiput posterior position

In occiput posterior position (sometimes called sunny-side up), the fetus is head first (vertex presentation) but is facing forward (toward the mother's pubic bone—that is, facing up when the mother lies on her back). This is a very common position that is not abnormal, but it makes delivery more difficult than when the fetus is in the occiput anterior position (facing toward the mother's spine—that is facing down when the mother lies on her back).

When a fetus faces up, the neck is often straightened rather than bent,which requires more room for the head to pass through the birth canal. Delivery assisted by a vacuum device or forceps or cesarean delivery may be necessary.

Breech presentation

In breech presentation, the baby's buttocks or sometimes the feet are positioned to deliver first (before the head).

When delivered vaginally, babies that present buttocks first are more at risk of injury or even death than those that present head first.

The reason for the risks to babies in breech presentation is that the baby's hips and buttocks are not as wide as the head. Therefore, when the hips and buttocks pass through the cervix first, the passageway may not be wide enough for the head to pass through. In addition, when the head follows the buttocks, the neck may be bent slightly backwards. The neck being bent backward increases the width required for delivery as compared to when the head is angled forward with the chin tucked, which is the position that is easiest for delivery. Thus, the baby’s body may be delivered and then the head may get caught and not be able to pass through the birth canal. When the baby’s head is caught, this puts pressure on the umbilical cord in the birth canal, so that very little oxygen can reach the baby. Brain damage due to lack of oxygen is more common among breech babies than among those presenting head first.

In a first delivery, these problems may occur more frequently because a woman’s tissues have not been stretched by previous deliveries. Because of risk of injury or even death to the baby, cesarean delivery is preferred when the fetus is in breech presentation, unless the doctor is very experienced with and skilled at delivering breech babies or there is not an adequate facility or equipment to safely perform a cesarean delivery.

Breech presentation is more likely to occur in the following circumstances:

Labor starts too soon (preterm labor).

The uterus is abnormally shaped or contains abnormal growths such as fibroids .

Management of Brow, Face, and Compound Malpresentations

Author: Meera Kesavan, MD

Mentor: Lisa Keder MD Editor: Daniel JS Martingano DO MBA PhD

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Fetal malpresentation, including brow, face, or compound presentations, complicates around 3-4% of all term births. Because these abnormal fetal presentations still are cephalic, many such cases result in vaginal deliveries, yet there are increased risks for adverse outcomes, including cesarean delivery resultant surgical complications, persistent malpresentation precluding vaginal delivery, and abnormal labor resulting in arrest of dilation or descent.

These fetal malpresentation are differentiated in the following ways:

In face presentations, the presenting part is the mentum, which is further divided based on its position, including mentum posterior, mentum transverse or mentum anterior positions. This typically occurs because of hyperextension of the neck and the occiput touching the fetal back. Mentum anterior malpresentations can potentially achieve vaginal deliveries, whereas mentum posterior malpresentations cannot.
In brow presentations, there is less extension of the fetal neck as in face presentations making the leading fetal part being the area between the anterior fontanelle and the orbital ridges. These presentations are uncommon and are managed similarly to face presentations. Brow presentation can be further described based on the position of the anterior fontanelle as frontal anterior, posterior, or transverse.
Compound presentation is defined as the leading fetal part, including a fetal extremity, alongside a cephalic or breech presentation. Management of compound presentations is expected (and often incidentally noted following delivery) because the extremity will often either retract as the head descends or will feasibly allow for delivery in its current position, with manipulation attempts to reduce the compound presentation usually avoided.

Risk factors for brow and face presentations include fetal CNS malformations, congenital or chromosomal anomalies, advanced maternal age, low birthweight, abnormal maternal pelvic anatomy (e.g. contracted pelvis, cephalopelvic disporotion, platypelloid pelvis, etc.) and nulliparity. non-Hispanic White women have the highest risk for malpresentation, whereas non-Hispanic Black women have the lowest risk.

Diagnosis usually is made during the second stage of labor while performing routine vaingla examinations and involves palpation of the abnormal leading fetal part (forehead, orbital ridge, orbits, nose, etc.) Obstetric ultrasound can additionally provide complimentary information to support these diagnoses and distinguish from other fetal malpresentations or malpositions. In face presentation, the mentum (chin) and mouth are palpable.

Management considerations for face, brow, and compounds presentations are unique with compound presentations having higher rates of vaginal delivery and lower complications as compared to either brow or face presentations.

For brow presentations, approximately 30-40% of brow presentations will convert to a face presentation, and about 20% will convert to a vertex presentation. Anterior positions have the possibility of vaginal deliveries and can be managed by usual labor management principles, whereas mentum posterior positions are indications for cesarean delivery.
For face presentations, the likelihood of vaginal delivery depends on the orientation of the mentum, with mentum anterior being most suitable for vaginal delivery. If the fetus is mentum posterior, flexion of the neck is precluded and results in the inability of fetal descent.
For compound presentations, management is expectant and manipulation of the leading extremities should be avoided. Most cases of compound presentation result in vaginal deliveries. For term deliveries, compound presentations with parts other than the hand are unlikely to result in safe vaginal delivery.

Labor management for brow and face presentation overall involves continuous fetal heart rate monitoring and repeat clinical assessments, given the increased potential of fetal complications as noted. Caution should be used with internal monitoring devices, which can cause ophthalmic injury or trauma to the presenting fetal parts, with the use of fetal scalp electrodes discouraged and intrauterine pressure catheters acceptable with appropriate clinical judgment and feasibility.

Midforceps, breech extraction, and manual manipulation are not recommended and increase the risk of maternal and neonatal morbidity.

Neonatal outcomes for both face and brow presentations include facial edema, bruising, and soft tissue trauma. Complications of compound presentation specifically include umbilical cord prolapse and injury to the presenting limb. With appropriate management, neonatal and maternal morbidity for face, brow, and compound presentations are low.