Ultrasound estimate of amniotic fluid volume: color Doppler overdiagnosis of oligohydramnios.

OBJECTIVE: To determine if concurrent use of color Doppler affects ultrasound estimates of amniotic fluid (AF) volume.

METHODS: Study gravidas underwent ultrasound estimations of AF volume subjectively (visualization without measurements) and objectively (using amniotic fluid index [AFI]) and single-deepest pocket techniques, without and with concurrent color Doppler. Amniocentesis with the dye-dilution technique to measure actual AF volume was utilized for comparison.

RESULTS: Sixty-seven women at a mean gestational age of 37.1 +/- 2.5 weeks were entered into this investigation between June 1999 and March 2000. Dye-determined AF volume was classified as low in 18 patients and as high in seven, with the remaining 42 within normal range. Using either ultrasound technique with color Doppler produced significantly lower estimates of AF volume (9.3 +/- 4.9) compared to those without color ([11.6 +/- 5], P <.001) for the AFI and (3.7 +/- 1.5) with color compared to those without color ([4.5 +/- 1.5], P <.003) for the single-deepest pocket. Using AFI without color identified two of 67 (3%) of the pregnancies as having low fluid compared to 14 of 67 ([21%] P =.002) using color. The increased classification of oligohydramnios with color did not accurately identify a greater number of dye-determined low volumes; instead, the AFI with color mislabeled nine pregnancies with normal fluid as low. The diagnosis of dye-determined low and high fluid volumes was not significantly different with or without color.

CONCLUSION: Concurrent use of color Doppler with AFI measurements leads to the overdiagnosis of oligohydramnios.