目的　探讨产前 B超测定羊水平段诊断羊水过少的最佳界值。方法　对妊娠≥ 36周的孕妇进行 B超测定羊水最大平段 ,剖宫产时实际测定羊水量 ,确定 2 .0 cm、2 .3cm、2 .6 cm、3.0 cm、3.3cm、3.5 cm、3.8cm等 7个界点 ,分别计算其敏感性、特异性、阳性预测值和阴性预测值 ,对各界点的敏感性和 (1-特异性 )作受试者工作特性曲线。结果　当B超测定羊水平段界点为 3.3cm时 ,可获得较高的诊断敏感性和特异性 ,其值为 80 .5 6 %和 78.79%。结论　 B超测定羊水平段界点值为 3.3cm时 ,可产前诊断为羊水过少 Objective To explore the best value of diagnosis of oligohydramnios by prenatal B-ultrasound in sheep’s level. Methods Pregnant women with gestational age ≥ 36 weeks were tested for the largest segment of amniotic fluid by ultrasonography. The amniotic fluid volume was measured at cesarean section. The amount of amniotic fluid was determined to be 2.0 cm, 2.3 cm, 2.6 cm, 3.0 cm, 3.3 cm, 3.5 cm, 3.8 cm and other seven boundaries, respectively, the sensitivity, specificity, positive predictive value and negative predictive value of the various points of the sensitivity and (1-specific) as the working characteristics of the receiver curve. Results The sensitivity and specificity of the diagnosis of B-ultrasonography at a 3.3cm cut-off point were 80.66% and 78.79%, respectively. Conclusion B-measurement sheep cut-off point value of 3.3cm, prenatal diagnosis of oligohydramnios