Do semiquantitative amniotic fluid indexes reflect actual volume?

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Diagnostic Imaging

Background:

• Accurate assessment of amniotic fluid volume is crucial for fetal well-being.
• Semiquantitative ultrasonographic methods are commonly used but their correlation with actual volume needs validation.

Purpose of the Study:

• To evaluate the accuracy of semiquantitative ultrasonographic measures (amniotic fluid index and maximal amniotic fluid vertical pocket) in reflecting actual amniotic fluid volumes.
• To compare the efficacy of amniotic fluid index versus maximal amniotic fluid vertical pocket in estimating amniotic fluid volume.

Main Methods:

• Fifty near-term patients with normal visual amniotic fluid estimates underwent ultrasound measurements (amniotic fluid index, maximal amniotic fluid vertical pocket) prior to amniocentesis.
• Intra-amniotic injection of paraaminohippurate solution followed by spectrophotometric assay quantified actual amniotic fluid volume.
• Oligohydramnios (< 300 ml) and polyhydramnios (> 2000 ml) were defined.

Main Results:

• Both amniotic fluid index and maximal amniotic fluid vertical pocket showed positive correlations with quantitative amniotic fluid volume (r=0.75 and r=0.60, respectively).
• True-positive rates for oligohydramnios were 100% for AFI (<5 cm) and 0% for MVP (<2 cm), with 0% false-positive rates for both.
• True-positive rates for polyhydramnios were 0% for both methods, with false-positive rates of 16% for AFI (>20 cm) and 24% for MVP (>8 cm).

Conclusions:

• The amniotic fluid index is a slightly more accurate indicator of actual amniotic fluid volume compared to the maximal amniotic fluid vertical pocket.
• Both ultrasonographic methods tend to overestimate amniotic fluid volume at the higher end of the normal range.