Subjective ultrasonographic assessment of amniotic fluid depth: comparison with the amniotic fluid index

The purpose of this study was to evaluate the ability to identify abnormalities in amniotic fluid volume by subjective ultrasonographic assessment compared to a semiobjective method. In 886 consecutive ultrasound examinations subjective assessment of the amniotic fluid volume was performed and graded into 3 categories: normal, decreased, and increased. Following that, a four-quadrant sum (amniotic fluid index) was performed by the same experienced ultrasonographer and divided into 3 categories using the 5th and 95th percentiles. The sensitivity of the subjective analysis to diagnose a decreased amniotic fluid volume when compared with the amniotic fluid index was 58% (95% confidence interval, CI: 40-70%), with a false-positive rate of 17% (CI 8-32%). The sensitivity of the subjective analysis to diagnose an increased amniotic fluid volume when compared with the amniotic fluid index was 100% (CI 70-100%). However, the false-positive rate was 74% (CI 55-85%). Diagnosis of a normal amount of amniotic fluid by the subjective technique had a sensitivity of 96% (CI 95-97%) and a false-positive rate of 3% (CI 2-4%). Subjective ultrasonographic assessment of the amniotic fluid volume may serve as a screening test for the experienced ultrasonographer. However, when a decreased or increased amount of amniotic fluid volume is suspected, one may elect to use the amniotic fluid index for confirmation of the subjective impression.