Ultrasonographic assessment of amniotic fluid does not reflect actual amniotic fluid volume.
OBJECTIVE
Our objective was to compare the ability of two methods of amniotic fluid assessment (two-diameter amniotic fluid pocket versus the amniotic fluid index) to predict oligohydramnios (actual amniotic fluid volume < 500 ml) or polyhydramnios (actual amniotic fluid volume > 1500 ml).


METHODS
The amniotic fluid index and the two-diameter amniotic fluid pocket were assessed before amniocentesis and determination of amniotic fluid volume with the dye (aminohippurate sodium)-dilution technique. To assess the detection of either oligohydramnios or polyhydramnios, the areas under the receiver-operator characteristic curves (+/-SE) were estimated by the point-to-point trapezoidal method of integration. Prediction limits were calculated by regression analysis of amniotic fluid index or two-diameter amniotic fluid pocket versus actual amniotic fluid volume and determination of 95th percentile ranges for amniotic fluid volume.


RESULTS
We studied 144 patients with a mean (+/-SD) gestational age of 31.7 +/- 5.5 weeks; mean (+/-SD) amniotic fluid index and two-diameter amniotic fluid pocket were 12.6 +/- 6.1 cm and 21.2 +/- 18.4 cm2, respectively. Mean (+/-SD) actual amniotic fluid volume was 722 +/- 735 ml (range 101 to 4318 ml). The areas under the four receiver-operator characteristic curves were not significantly different from the nondiagnostic line (p < 0.05). Regression slopes (r values) for amniotic fluid index and two-diameter amniotic fluid pocket versus actual amniotic fluid volume were 0.34 and 0.23, respectively. Calculation of the prediction limit for 95% confidence that oligohydramnios is absent requires that the amniotic fluid index be 30 cm and the two-dimension amniotic fluid pocket be 90 cm2, both thresholds of which are currently considered to represent clinical polyhdramnios.


CONCLUSIONS
Both amniotic fluid index and two-dimension amniotic fluid pocket appear to be inaccurate predictors of actual oligohydramnios or polyhydramnios when compared with dye-dilution calculations of actual amniotic fluid volume.
Chauhan
S P
SP
Department of Obstetrics and Gynecology, Medical College of Georgia, Augusta 30912-3350, USA.
Magann
E F
EF
Morrison
J C
JC
Whitworth
N S
NS
Hendrix
N W
NW
Devoe
L D
LD
D000328:Adult; D000618:Aminohippuric Acids; D000649:Amniocentesis; D000653:Amniotic Fluid / Q000000981:diagnostic imaging*; D004396:Coloring Agents; D005260:Female; D005865:Gestational Age; D006801:Humans; D007201:Indicator Dilution Techniques; D016104:Oligohydramnios / Q000000981:diagnostic imaging*; D006831:Polyhydramnios / Q000000981:diagnostic imaging*; D011247:Pregnancy; D012044:Regression Analysis; D014463:Ultrasonography
D000618:Aminohippuric Acids; D004396:Coloring Agents