Face presentation is diagnosed by vaginal examination and palpation of facial features. A breech may be mistaken for a face presentation. Namely, the anus may be mistaken for the mouth, and the ischial tuberosities for the malar prominences. Digital diferentiation is described in Chapter 28 (p. 540). Radiographically, demonstration of the hyperextended head with the facial bones at or below the pelvic inlet is characteristic.
Cruikshank and White (1973) reported an incidence of 1 in 600, or 0.17 percent. As shown in Table 22-1 (p. 422), among more than 70,000 singleton newborns delivered at Parkland Hospital, approximately 1 in 2000 had a face presentation at delivery.
Causes of face presentations are numerous and include conditions that favor extension or prevent head lexion. Preterm fetuses, with their smaller head dimensions, can engage before conversion to vertex position (Shafer, 2006). In exceptional instances, marked enlargement of the neck or coils of cord around the neck may cause extension. Bashiri and associates (2008) reported that fetal malformations and hydramnios were risk factors for face or brow presentations. Anencephalic fetuses naturally present by the face.
Extended neck positions develop more frequently when the pelvis is contracted or the fetus is very large. In a series of 141 face presentations studied by Hellman and coworkers (1950), the incidence of inlet contraction was 40 percent. his high incidence of pelvic contraction should be kept in mind when considering management.
High parity is a predisposing factor for face presentation (Fuchs, 1985). In these cases, a pendulous abdomen permits the back of the fetus to sag forward or laterally, often in the same direction in which the occiput points. his promotes extension of the cervical and thoracic spine.
Mechanism of Labor
Face presentations rarely are observed above the pelvic inlet. Instead, the brow generally presents early and is usually converted to present the face after further extension of the neck during descent. he mechanism of labor in these cases consists of the cardinal movements of descent, internal rotation, and flexion, and the accessory movements of extension and external rotation (Fig. 23-7). Descent is brought about by the same factors as in cephalic presentations. Extension results from the relation of the fetal body to the delected head, which is converted into a two-armed lever, the longer arm of which extends from the occipital condyles to the occiput. When resistance is encountered, the occiput must be pushed toward the back of the fetus while the chin descends.
The objective of internal rotation of the face is to bring the chin under the symphysis pubis. Only in this way can the neck traverse the posterior surface of the symphysis pubis. If the chin rotates directly posteriorly, the relatively short neck cannot span the anterior surface of the sacrum, which measures about 12 cm in length. Moreover, the fetal brow (bregma) is pressed against the maternal symphysis pubis. This position precludes lexion necessary to negotiate the birth canal. Hence, as discussed earlier, birth of the head from a mentum posterior position is impossible unless the shoulders enter the pelvis at the same time, an event that is impossible except when the fetus is extremely small or macerated. Internal rotation results from the same factors as in vertex presentations.
After anterior rotation and descent, the chin and mouth appear at the vulva, the undersurface of the chin presses against the symphysis, and the head is delivered by lexion. The nose, eyes, brow (bregma), and occiput then appear in succession over the anterior margin of the perineum. ter birth of the head, the occiput sags backward toward the anus. Next, the chin rotates externally to the side toward which it was originally directed, and the shoulders are born as in cephalic presentations.
Edema may sometimes significantly distort the face. At the same time, the skull undergoes considerable molding, manifested by an increase in length of the occipitomental diameter of the head.