(Ultrasound Review) A comparison of subjective versus objective ultrasonic evaluation of amniotic fluid (AF) volume in pregnancies of less than 24 weeks’ gestation showed no significant difference between the two methods, according to researchers from the University of Mississippi Medical Center in Jackson.
Three examiners of varying experience used a number of objective measurement methods to study 42 women, and the results were recently published in Journal of Ultrasound in Medicine. The primary objective measurement used in this study, the AF index, was calculated by adding the largest vertical pocket of AF without fetal parts or umbilical cord for each quadrant.
All of the women studied had fetuses with chromosomal or structural abnormalities or both. During amniocentesis for administration of prostaglandin prior to pregnancy termination, a dye dilution study was performed to determine AF volume. This indirect method of AF volume measurement involves using a diazo-dye reaction-spectrophotometric technique developed by Charles and Jacoby, and was used as the standard for verifying the two ultrasonic methods of AF volume assessment.
Results showed that only half of the cases of oligohydramnios (eight pregnancies) were accurately estimated using the subjective determinations of AF volume, and the combined objective estimates were accurate in only 31% of cases. There were five cases of polyhydramnios, and the one case correctly identified was achieved using both objective and subjective methods. No comment was made on the proven accuracy of the dye dilution study that was used as the standard.
And so, when the AF volume is normal, both subjective and objective AF estimates achieve a similar, accurate result, but neither of the methods was accurate for low or high AF volumes. The authors concluded that "the accuracy of amniotic fluid volume assessment in pregnancies of less than 24 weeks is not influenced by the level of operator experience or the type of ultrasonic measurement." Also, "AF volume is readily confirmed both subjectively and objectively, but the extremes of AF volume are poorly identified."
"Subjective versus objective evaluation of amniotic fluid volume of pregnancies of less than 24 weeks’ gestation"
Everett F Magann et al
Ob-Gyn Publication Office, University of Mississippi Medical Center, 2500 North State St., Jackson, MS 39216, USA
J Ultrasound Med 2000 (March); 20: 191–195
By Ultrasound Review
April 17, 2001
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