课件：第九章异常分娩.ppt

* With mentum anterior presentation, oxytocin augmentation may be used for arrested labor if cephalopelvic disproportion can be ruled out. Delivery may be accomplished by spontaneous vaginal delivery, use of low forceps to rotate to the mentum anterior position, or cesarean section for arrested labor. There is little or no place for manual flexion of the fetal head or manual rotaion from the mentum posterior position to the mentum anterior position. * The above mechanisms of labor in the term infant can occur only if the mentum is anterior. If the mentum is posterior, the fetal neck is too short to span the length of the maternal sacrum and is already at the point of maximal extension. To deliver, the fetal shoulders must also enter the pelvis, although the head still cannot deliver because it cannot extend further through the symphysis. Mentum posterior positions in average-size fetuses are not deliverable vaginally as they are unable to extend. Arrested labor is typical when spontaneous rotation to the mentum anterior position fails to occur. * Breech presentation is diagnosed by ultrasound, Leopolds maneuver, or vaginal examination. At term, 3% to 4% of deliveries are in the breech presentation. Because of the higher incidence of congenital anomalies in breech versus vertex presentations in term or preterm gestations, a morphology ultrasound is recommended to rule out this possibility. Breech presentation is always complicated with increased perinatal morbidity, 3-8 folds higher than vertex presentation. Fetal position in breech presentation is determined by using the sacrum as the fetal point of reference to the maternal pelvis. Six positions are recognized: left sacrum transverse, right sacrum transverse left sacrum anterior, left sacrum posterior, right sacrum anterior and right sacrum posterior. * Before 30 weeks, the fetus is small enough in relation to intrauterine volume to rotate from cephalic to breech presentation and back again with relative ease. A