The third maneuver aids confirmation of fetal presentation. The thumb and ingers of one hand grasp the lower portion of the maternal abdomen just above the symphysis pubis. If the presenting part is not engaged, a movable mass will be felt, usually the head. The diferentiation between head and breech is made as in the first maneuver.
The fourth maneuver helps determine the degree of descent. he examiner faces the mother's feet, and the ingertips of both hands are positioned on either side of the presenting part. They exert inward pressure and then slide caudad along the axis of the pelvic inlet. In many instances, when the head has descended into the pelvis, the anterior shoulder or the space created by the neck may be diferentiated readily from the hard head.
Abdominal palpation can be performed throughout the latter months of pregnancy and during and between the contractions of labor. At least in the past, according to Lydon-Rochelle plished readily. Second, if the vertex is presenting, the fingers are directed posteriorly and then swept forward over the fetal head toward the maternal symphysis (Fig. 22-9). During this movement, the fingers necessarily cross the sagittal suture, and its linear course is delineated. Next, the positions of the two fontanels, found at either end of the sagittal suture, are ascertained. For this, fingers are passed to the most anterior extension of the sagittal suture, and the fontanel encountered there is examined and identiied. hen, the fingers pass along the suture to the other end of the head until the other fontanel is felt and diferentiated (Fig.
10). Last, the station, or extent to which the presenting part has descended into the pelvis, can also be established at this time (p. 436). Using these maneuvers, the various sutures and fontanels are determined (Fig. 29-1, p. 554).
identification, especially in obese women or in women with muscular
FIGURE 22-9 Locating the sagittal suture by vaginal examination.
abdominal walls. Compared with digital examinations, sonography for fetal head position determination during secondstage labor is more accurate (Ramphul, 2014; Wiafe, 2016).
In most cases, the vertex enters the pelvis with the sagittal suture lying in the transverse pelvic diameter. The fetus enters the pelvis in the let occiput transverse (LO) position more commonly than right occiput transverse (RO) position (Caldwell, 1934). In occput anterior positions-LOA or ROA-either the head enters the pelvis with the occiput rotated 45 degrees anteriorly from the transverse position, or this rotation occurs subsequently. The mechanism oflabor in all these presentations is usually similar.
The positional changes of the presenting part required to navigate the pelvic canal constitute the mechanisms of labor. The cardinal movements of labor are engagement, descent, lexion, internal rotation, extension, external rotation, and expulsion
During labor, these movements not only are sequential but also show great temporal overlap. For example, as part of engagement, there is both flexion and descent of the head. It is impossible for the movements to be completed unless the presenting part descends simultaneously. Concomitantly, uterine contractions efect important modifications in fetal attitude, or habitus, especially ater the head has descended into the pelvis. These changes consist principally of fetal straightening, with loss of dorsal convexity and closer application of the extremities to the body. As a result, the fetal ovoid is transformed into a cylinder, with the smallest possible cross section typically passing through the birth canal.
FIGURE 22-10 Differentiating the fontanels by vaginal examination.