The fetus occupies less
than half of the intrauterine volume until approximately 22 weeks in the
normal pregnancy. Thereafter the fetus progressively occupies a larger proportion
of the intrauterine volume.
This is a qualitative
assessment of amniotic fluid volume and is therefore not standardized (1).
intraobserver variability is reported to be very low.
Single Deepest Pocket
dimensions of the largest vertical pocket of amniotic fluid.
et.al.1981. : Pocket of fluid
<1cm = oligohydramnios
1-2cm = decreased fluid
2-8cm = normal
>8cm = polyhydramnios (3,4)
Many authors question
the 1cm rule as being too restrictive (5).
cut-off criteria for oligohydramnios (6):
Divide the uterus into
four quadrants using the linea nigra as the vertical axis and the
umbilicus as the horizontal axis
The pocket with the
largest vertical dimension is measured in each quadrant.
Sum of all four
measurements = AFI
<5cm = very low (oligohydramnios)
5.1-8cm = low
8.1-25cm = normal
>25cm = polyhydramnios
Controversies in cut-off
criteria for oligohydramnios:
< 5 cm (this
represents <1st centile) (12)
centile for gestational age (AFI values of 7.1 and 9.7 cm) (15)
< 7 cm (16)
< 8 cm (17)
considered an AFI > 5 and < 10 as borderline. (18).
Easy to perform.
approach than amniotic fluid assessment.
training to perform and is ideally suited to real time ultrasound.
Provides a frame of
reference for the inexperienced sonographer.
Gives a better
assessment of amniotic fluid volume than does the single deepest pocket
measurement, as the sum of all four quadrants correlate more closely
with volume than by using a single measurement.
applied by the sonographer with the transducer on the patients abdomen
can decrease the height of a pocket of fluid.
anterior reverberation artifacts may obscure amniotic fluid situated
anteriorly. It may also be difficult to visualize lateral pockets due
to the position of the transducer.
in the third
trimester the umbilical cord may be extremely lucent and without duplex
or color doppler, cord filled pockets of amniotic fluid may be included
in the measurement.
Dildy et.al. (23)
reported that the AFI overestimated the actual fluid volume byas much as 88.7% at lower volumes.
(24) compared semi-quantitative methods (AFI and two-diameter pocket)
with fluid assessment at dye dilution amniocentesis and concluded that
the range of the 95% confidence intervals is so wide that sonographic
assessment is not a reasonable reflection of the actual amniotic fluid
Magaan et. al.
(25) reported a sensitivity of 6.7% in predicting true oligohydramnios
(<500 ml) (25)
imprescise in the detection of oligohydramnios and using multiple
assessments did not add to the overall accuracy (26).
movements may be a problem as large pockets may be replaced by multiple
small pockets between the extremities.
Pockets with large
vertical dimensions and small width's will exaggerate the AFI.
What is the
significance of a full fetal bladder in the presence of ologohydramnios
(6). Should this fluid be included in the AFI estimation as it will
ultimately be excreted and form part of the fluid estimation.
hydration have any effect on the AFI?
– vertical X horizontal < 15 cm (22).
Goldstein RB, Filly RA. Sonographic
estimation of amniotic fluid volume: Subjective assessment versus pocket
measurements. J Ultrasound Med 1988; 7:363.
Manning FA, Hill LM, Platt
LD. Quantitative amniotic fluid volume determination by ultrasound:
Antepartum detection of intrauterine growth retardation. Am J Obstet
Gynecol 1981; 139: 254-258.
Chamberlain P. Amniotic
fluid volume: Ultrasound assessment and clinical significance. Semin
Perinatol 1985; 9:163-167.
Varma TR, Bateman S, Patel
RH et.al. Ultrasound evaluation of amniotic fluid: outcome of pregnancies
with severe oligohydramnios. Int J Gynecol Obstet 1988; 27:185-192.
Hoddick WK, Callen PW,
Filly RA et.al. Ultrasonographic determination of qualitative amniotic
fluid volume in intrauterine growth retardation. Reassessment of the 1cm
rule. Am J Obstet Gynecol 1984; 149:758-762.
Sherer DM, Langer O.
Editorial Oligohydramnios: use and misuse in clinical management.
Ultrasound Obstet Gynecol 2001;18:411-419.
Mercer LJ, Brown LG, Petres
RE et.al. A survey of pregnancies complicated by decreased amniotic fluid.
Am J Obstet Gynecol 1984;149:355-356.
Chamberlain PF, Manning FA,
Morrison I et.al. Ultrasound evaluation of amniotic fluid volume. I. The
relationship of marginal and decreased amniotic fluid volumes to perinatal
outcome.Am J Obstet Gynecol 1984;150:245-249.
Manning FA, Harmon CR,
Morrison I et.al. Fetal assessment based on fetal biophysical profile
scoring. IV> An analysis of perinatal morbidity and mortality. Am J
Obstet Gynecol 1990;162:703-709.
Halperin ME, Fong KW, Zalev
AH et.al. Reliability of amniotic fluid volume estimation from
ultrasonograms: intra-observer and interobserver variation before and
after the establishment of criteria. Am J Obstet Gynecol 1985;153:264-267.
Patterson RM, Prihoda TJ,
Pouliot MR. Sonographic amniotic fluid measurement and fetal growth
retardation: A reappraisal. Am J Obstet Gynecol 1987; 157: 1406-1410.
Phelan JP, Smith CV,
Broussard P, et.al. Amniotic fluid volume assessment with the
four-quadrant technique at weeks gestation. J Reprod Med 1987; 32:540-542.
Rutherford SE, Phelan JP,
Smith CV, et.al. The four-quadrant assessment of amniotic fluid volume: an
adjunct to antepartum fetal heart rate testing. Obstet Gynecol 1987;
Phelan JP, AhnMO,
Smith CV, et.al. Amniotic fluid index measurements during pregnancy. J
Reprod Med 1987; 32:601-604.
Moore TR, Cayle JE. The amniotic fluid
index in normal human pregnancy. Am J Obstet Gynecol 1990;162:1168-1173.
Dizon-Townson D, Kennedy
KA, DildyGA et.al. Amniotic fluid index and
morbidity. Am J Perinatol 1996;13:231-234.
Jeng CJ, Lee JF, Wang KG
et.al. Decreased amniotic fluid index in term pregnancy: clinical
significance. J reprod Med 1992;37:789-792.
Rodgers MS, Wang CC. A
comparison of three ultrasound estimates of intrapartum oligohydramnios
for prediction of fetal hypoxia-reperfusion injury. Early Hum Dev
Phelan JP, Park YW, AhnMO
et.al. Polyhydramnios and perinatal outcome. J Perinatol 1990; 10:347-350.
Rutherford SE, Smith CV,
Phelan JP, et.al. Four-quadrant assessment of amniotic fluid volume. J
Reprod Med 1987; 32:587-589.
Crawford RA, Spender JAD, et.al. Intrapartum amniotic fluid index and its
relationship to fetal distress. Am J Obstet Gynecol 1992; 166:78-82
Banks EH, Miller DA. Perinatal
risks associated with borderline amniotic fluid index. Am J Obstet Gynecol
Lira N, Moise KJ et.al. Amniotic fluid volume assessment: comparison of
ultrasonographic assessment versus direct measurements with a dye dilution
technique in human pregnancy. Am J Obstet Gynecol 1992;167:986-994.
Chauhan SP, Magaan EF,
Morrison JC et.al. Ultrasonographic assessment of amniotic fluid does not
reflect actual amniotic fluid volume. Am J Obstet Gynecol
Magaan EF, Nolan TE, Hess
LW et.al. Measurement of amniotic fluid volume: accuracy of
ultrasonography techniques. Am J Obstet Gynecol 1992;167:1533-1537.
Magaan EF, Chauhan SP, WhitworthNS
et.al. Do multiple measurements employing different ultrasonic techniques
improve the accuracy of amniotic fluid volume assessment? Aust NZ J Obstet