On vaginal examination, in the early stages of labor, if the side of the thorax can be reached, it may be recognized by the "gridiron" feel of the ribs. With further dilation, the scapula and the clavicle are distinguished on opposite sides of the thorax. The position of the axilla indicates the side of the mother toward which the shoulder is directed.
(0.3 percent) at both the Mayo Clinic and the University of Iowa Hospital (Cruikshank, 1973; Johnson, 1964). This is remarkably similar to the incidence at Parkland Hospital of approximately 1 in 335 singleton fetuses.
Some of the more common causes of transverse lie include: (1) abdominal wall relaxation from high parity, (2) preterm fetus, (3) placenta previa, (4) abnormal uterine anatomy, (5) hydramnios, and (6) contracted pelvis.
Women with four or more deliveries have a tenfold incidence of transverse lie compared with nulliparas. A relaxed and pendulous abdomen allows the uterus to fall forward, delecting the long axis of the fetus away from the axis of the birth canal and into an oblique or transverse position. Placenta previa and pelvic contraction act similarly. A transverse or oblique lie occasionally develops in labor from an initial longitudinal position.
Mechanism of Labor
Spontaneous delivery of a fully developed newborn is impossible with a persistent transverse lie. After rupture of the membranes, if labor continues, the fetal shoulder is forced into the pelvis, and the corresponding arm frequently prolapses (Fig. 23-10). After some descent, the shoulder is arrested by the margins of the pelvic inlet. As labor continues, the shoulder is impacted irmly in the upper part of the pelvis. he uterus then contracts vigorously in an unsuccessful attempt to overcome the obstacle. With time, a retraction ring rises increasingly higher and becomes more marked. With this neglected transverse lie, the uterus will eventually rupture. Even without this complication, morbidity is increased because of the frequent association
FIGURE 23-10 Neglected shoulder presentation. A thick cular band forming a pathological retraction ring has developed just above the thin lower uterine segment. The force generated during a uterine contraction is directed centripetally at and above the level of the pathological retraction ring. This serves to stretch further and possibly to rupture the thin lower segment below the retraction ring.
with placenta previa, the increased likelihood of cord prolapse, and the necessity for major operative eforts.
If the fetus is small-usually < 800 g-and the pelvis is large, spontaneous delivery is possible despite persistence of the abnormal lie. The fetus is compressed with the head forced against its abdomen. A portion of the thoracic wall below the shoulder thus becomes the most dependent part, appearing at the vulva. he head and thorax then pass through the pelvic cavity at the same time. he fetus, which is doubled upon itself and thus sometimes referred to as condupLicato corpore, is expelled.
Active labor in a woman with a transverse lie is usually an indication for cesarean delivery. Before labor or early in labor, with the membranes intact, attempts at external version are worthwhile in the absence of other complications. If the fetal head can be maneuvered by abdominal manipulation into the pelvis, it should be held there during the next several contractions in an attempt to ix the head in the pelvis.
With cesarean delivery, because neither the feet nor the head of the fetus occupies the lower uterine segment, a low transverse incision into the uterus may lead to diicult fetal extraction. his is especially true of dorsoanterior presentations. herefore, a vertical hysterotomy incision is often indicated .