Amniotic fluid volume assessment: Comparison of ultrasonographic estimates versus direct measurements with a dye-dilution technique in human pregnancy

Abstract

OBJECTIVE: The purpose of our study was to compare the accuracy of clinical ultrasonographic techniques of amniotic fluid volume assessment with a dye-dilution technique. STUDY DESIGN: We compared amniotic fluid volume as measured by ultrasonographic techniques with a dye-dilution method in 50 women undergoing amniocentesis during the third trimester. Thirteen separate ultrasonographic techniques, including the amniotic fluid index, were evaluated with regression analysis. RESULTS: Amniotic fluid volumes as determined by dye-dilution ranged between 129 and 4444 ml. The amniotic fluid index overestimated the actual volume by as much as 88.7% at lower volumes and underestimated the actual volume by as much as 53.9% at higher volumes. CONCLUSIONS: Differences in measurement error between the other ultrasonographic methods and the amniotic fluid index did not appear to be sufficient to warrant changes in current clinical practice. A major source of error in ultrasonographic amniotic fluid volume assessment is that one-dimensional measurements are used to estimate the volume of a complex, three-dimensional object. ( Am J Obstet Gynecol 1992;167:986–94.)