探讨探头下孕妇腹壁低频振动法诊断膜状胎盘的价值。

选择怀疑膜状胎盘及其他胎盘异常的孕妇36例，采用探头下孕妇腹壁低频振动法进行检查，振动频率为3~5次/s，每次持续振动时间不超过3 s，然后立即对胎盘进行观察，记录胎盘内部回声的变化，并在同一位置再次测量胎盘的厚度，比较膜状胎盘与其他胎盘异常的回声特征。

36例胎盘异常者，胎盘娩出后最终确诊为完全性膜状胎盘2例，部分性膜状胎盘16例，胎盘血窦15例，胎盘绒毛膜血管瘤3例。完全性膜状胎盘和部分性膜状胎盘的膜状化部分在探头低频振动前和振动后超声声像图表现明显不同，均表现为由均匀一致的高回声变为漩动的高低回声相互变化的非均匀回声，呈流动状或漩涡状的"漩动状"胎盘。而非膜状化部分和胎盘其他异常在探头低频振动前后无此声像特征。

探头下孕妇腹壁低频振动法是识别与诊断膜状胎盘的有效方法。这种在低频振动后出现回声不均匀和明显"漩动状"的胎盘声像特征，是识别与诊断膜状胎盘的特征性声像，也是区别于胎盘其他异常的可靠鉴别诊断特征。

To study the value of the new method of abdominal wall low frequency vibration (AWLFV) by prenatal ultrasound in diagnosis and differential diagnosis of placenta membranacea (PM).

Thirty-six cases of abnormal placenta were enrolled into the study. AWLFV was used in all 36 cases. The vibration was conducted with a frequency of 3 to 5 times per second and a duration less than 3 seconds at a time. And then the placenta was immediately observed to record the placenta echogenicity changes, and in the same place the thickness of the placenta was measured. The echo characteristics of PM and other abnormal placenta was compared.

Thirty-six cases were finally diagnosed as complete PM in 2 cases, partial PM in 16 cases, placental sinus in 15 cases, and placental chorionic hemangioma in 3 cases. The echo characteristics of complete and partial PM were obviously different before and after AWLFV on ultrasonic image. The homogeneous echotexture of PM before AWLFV was changed immediately to the inhomogeneous echotexture after AWLFV. The ″spiral shape″ of the placenta was displayed. And in other plasental anomalies this feature was not observed before and after vibration.

The AWLFV is an effective method in diagnosis and differentiation of PM.