In the absence of a contracted pelvis and with efective labor, successful vaginal delivery usually will follow. Fetal heart rate monitoring is probably better done with external devices to avoid damage to the face and eyes. Because face presentations among term-size fetuses are more common when there is some degree of pelvic inlet contraction, cesarean delivery frequently is indicated. Attempts to convert a face presentation manually into a vertex presentation, manual or forceps rotation of a persistently posterior chin to a mentum anterior position, and internal podalic version and extraction are dangerous and should not be attempted. Low or outlet forceps delivery of a mentum anterior face presentation can be completed and is described in Chapter 29 (p. 562).
This rare presentation is diagnosed when that portion of the fetal head between the orbital ridge and the anterior fontanel presents at the pelvic inlet. As shown in Figure 23-8, the fetal head thus occupies a position midway between full lexion (occiput) and extension (face). Except when the fetal head is small or the pelvis is unusually large, engagement of the fetal head and subsequent delivery cannot take place as long as the brow presentation persists.
The causes of persistent brow presentation are the same as those for face presentation. A brow presentation is commonly unstable and often converts to a face or an occiput presentation (Cruikshank, 1973). The presentation may be recognized by abdominal palpation when both the occiput and chin can be palpated easily, but vaginal examination is usually necessary. The frontal sutures, large anterior fontanel, orbital ridges, eyes, and root of the nose are felt on vaginal examination, but neither the mouth nor the chin is palpable.
FIGURE 23-8 Brow posterior presentation.
With a very small fetus and a large pelvis, labor is generally easy. With a larger fetus, it is usually diicult. his is because engagement is impossible until there is marked molding that shortens the occipitomental diameter or more commonly, until the neck either lexes to an occiput presentation or extends to a face presentation. The considerable molding essential for vaginal delivery of a persistent brow characteristically deforms the head. he caput succedaneum is over the forehead, and it may be so extensive that identiication of the brow by palpation is impossible. In these instances, the forehead is prominent and squared, and the occipitomental diameter is diminished.
In transient brow presentations, the prognosis depends on the ultimate presentation. If the brow persists, prognosis is poor for vaginal delivery unless the fetus is small or the birth canal is large. Principles of management are the same as those for a face presentation.
In this position, the long axis of the fetus is approximately perpendicular to that of the mother. When the long axis forms an acute angle, an oblique lie results. The latter is usually only transitory, because either a longitudinal or transverse lie commonly results when labor supervenes. For this reason, the oblique lie is called an unstable lie in Great Britain.
FIGURE 23-9 Leopold maneuver performed on a woman with a fetal transverse lie, right acromiodorsoanterior position.
In a transverse lie, the shoulder is usually positioned over the pelvic inlet. The head occupies one iliac fossa, and the breech the other. This creates a shoulder presentation in which the side of the mother on which the acromion rests determines the designation of the lie as right or let acromial. And because in either position the back may be directed anteriorly or posteriorly, superiorly or inferiorly, it is customary to distinguish varieties as dorsoanterior and dorsoposterior (Fig. 23-9).
A transverse lie is usually recognized easily, often by inspection alone. The abdomen is unusually wide, whereas the uterine fundus extends to only slightly above the umbilicus. No fetal pole is detected in the fundus, and the ballottable head is found in one iliac fossa and the breech in the other. The position of the back is readily identifiable. When the back is anterior, a hard resistance plane extends across the front of the abdomen. When it is posterior, irregular nodulations representing fetal small parts are felt through the abdominal wall.