Ultrasound evaluation of amniotic fluid volume: methods and clinical accuracy.

Ultrasound evaluation of amniotic fluid volume (AFV) is frequently used to detect fetuses at high risk for an adverse outcome - an event that is often correlated with AFV abnormalities. As is well known, ultrasound is a non invasive procedure, which makes it ideal for application on a very large scale: in practice, it can be used for routine monitoring of all pregnancies and, not infrequently, for repeat AFV determination in those cases where there is the suspect of amniotic fluid abnormalities. Sonographic quantification of AFV, whether it is performed through a simple visual estimation or through biometric measurement of one or more amniotic fluid pockets, can never represent a true "quantitative" method and its actual reliability has not consistently been proved by scientific evidence. Moreover, even though ultrasound AFV evaluation is indispensable in the management of high-risk pregnancies, there is no consensus on which ultrasound index is the most accurate in predicting perinatal morbidity and mortality. The sonographer can evaluate AFV by directly observing amniotic fluid pockets and his experience is crucial for a high reliability of the procedure. When pathological AFV changes are present, especially if the examination is performed by a not so expert sonographer, biometric measurements (Single Deepest Pocket, Amniotic Fluid Index, Two-Diameter Pocket) with their respective reference ranges might be helpful in confirming the diagnosis of oligohydramnios or hydramnios. A complete review of all tests performances and confidences is made by the Authors.