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[单选题]
初产妇,孕41周,规律宫缩14小时入院。查:髂棘间径24cm, 骶耻外径19cm, 坐骨棘突出,坐骨棘间径9cm, 坐骨切迹小于2横指,坐骨结节间径8cm, 骶骨前面平直。枕左前位,胎心140次/分。肛查宫口开大4cm,S=0。小时后产妇呼叫腹痛难忍,检查:腹痛拒按,脉搏110次/分,呼吸28次/分,宫缩40”/1', 宫缩时胎心106次/分。阴道检查宫口开大5cm, S=0.112. 此时产程受阻的原因主要是()
A.骨盆入口狭窄
B.骨盆出口狭窄
C.中骨盆狭窄
D.扁平骨盆
E.漏斗骨盆
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