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Obstetrics & Gynecology:
Clinical Commentary

AMNIOTIC FLUID VOLUME ESTIMATION AND THE BIOPHYSICAL PROFILE: A CONFUSION OF CRITERIA

Magann, Everett F. MD; Isler, Christy M. MD; Chauhan, Suneet P. MD; Martin, James N. Jr MD

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Abstract

The biophysical profile (BPP) can be used as an initial test of fetal health and as a secondary back-up assessment of fetuses at risk of adverse outcomes when preliminary evaluations are not reassuring. The BPP evaluates five characteristics: fetal movement, tone, breathing, heart reactivity, and amniotic fluid (AF) volume estimation. Three of the most frequently used obstetric textbooks define adequate AF volume differently. In two of the three, the stated method of evaluating AF volume differs from that actually used by the referenced authors. We reviewed articles by Manning and found that his methodology changed from a 1-cm pocket in one plane to a 1-cm pocket in two perpendicular planes, and finally to a 2-cm vertical pocket with a 1-cm horizontal measurement. The 2 × 2-cm pocket is a fourth methodology that has been introduced recently. It is not known how often and in which groups each of the four methods has been used to evaluate abnormal AF volumes. The relevance and importance of determining precisely the ultrasound measurement actually used for investigations are emphasized by looking at women with AF indices ≤ 5. Fifty-three percent of those women had a 2 × 2 pocket, 72% had a 2 × 1 pocket, and 95% had a 1 × 1 pocket. The diagnosis of low fluid can lead to additional testing, hydration, and intervention, so the importance of a universal definition linked with pregnancy outcomes cannot be overemphasized.

Two of the most commonly used antenatal tests of fetal well-being are the biophysical profile (BPP) and the modified BPP. Both tests include an ultrasonic estimate of amniotic fluid (AF) volume. For the modified BPP an amniotic fluid index (AFI) is measured, and for the BPP the largest vertical pocket of AF is interpreted as absence of oligohydramnios. The AF volume is influenced by the condition that places the pregnancy at risk of adverse outcomes, and as the fluid decreases the risk increases, which makes estimation of AF volume an important component of the BPP.

© 2000 The American College of Obstetricians and Gynecologists

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