Reproducibility of measuring amniotic fluid index and single deepest vertical pool throughout gestation

• Published in: Prenatal diagnosis Vol. 35; no. 5; pp. 434 - 439
• Main Authors: Sande, J. A., Ioannou, C., Sarris, I., Ohuma, E. O., Papageorghiou, A. T.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-05-2015; Wiley Subscription Services, Inc
• Subjects: Adult; Amniotic Fluid - diagnostic imaging; Cohort Studies; Female; Humans; Observer Variation; Pregnancy; Pregnancy Trimester, Second; Pregnancy Trimester, Third; Prospective Studies; Reproducibility of Results; Ultrasonography, Prenatal - methods
• ISSN: 0197-3851; 1097-0223
• DOI: 10.1002/pd.4504

Objective
The aim of this study is to assess the intraobserver and interobserver reproducibility of measurement of amniotic fluid index (AFI) and single deepest vertical pool (SDVP), also known as the maximal vertical pocket.
Methods
A total of 175 fetuses were evaluated. For each fetus, two observers acquired duplicate sets of AFI and SDVP. Measurement differences were expressed as actual and percentage values. For all comparisons, Bland–Altman plots were used to compare differences, and limits of agreement were calculated.
Results
Intraobserver and interobserver agreement remained fairly constant with gestation, both for AFI and SDVP. The intraobserver limits of agreement for AFI were −5.2 to 5 cm or −39% to 37%; whereas for SDVP, these were −2.6 to 2.4 cm or −52% to 48%. The interobserver limits of agreement for AFI measurement were −7.3 to 7.1 cm or −54% to 53% and for SDVP measurement were −2.5 to 2.5 cm or −51% to 52%. Intraobserver coefficient of variation for SDVP was 14% and for AFI was 19%; the interobserver coefficient was 19% for both AFI and SDVP.
Conclusion
Limits of agreement for both methods are wide. The choice of method should be dictated by clinical considerations other than method reproducibility. © 2014 John Wiley & Sons, Ltd.
What's already known about this topic?
Amniotic fluid is a key indicator of fetal well‐being in the second half of gestation. Detection of abnormal amniotic fluid volume (AFV) is significant because it often correlates with adverse outcomes. Measurement of AFV can be carried out via invasive or noninvasive techniques. Ultrasound is widely accepted as the method of choice clinically, as it is easily accessible and safe. However, it is operator dependent, semiquantitative, and less accurate than invasive methods such as dye dilution techniques. There are two common ways to measure AFV with ultrasound: the amniotic fluid index (AFI) and single deepest vertical pool (SDVP). There is no consensus as to whether AFI or SDVP is the more reproducible method for measuring AFV throughout gestation. Therefore, choice is currently on the basis of clinical preference or local protocols.
The aim of this study is to establish and compare the reproducibility of the most commonly used two methods, AFI and SDVP, throughout gestation.
What does this study add?
This is a large study of 175 fetuses and 1400 measurements. In this study, we presented the intraobserver and interobserver variation of AFI and SDVP measurement, both in actual measurement difference and percentage difference values. The limits of agreement are wide for both AFI and SDVP and none is consistently superior to the other. Further work is warranted in order to standardize a reproducible method to assess AFV. Until then, care should be taken in clinical practice in the interpretation of an abnormal AFV value.