196 Moderate-severe polyhydramnios: cutoffs for deepest vertical pocket corresponding to amniotic fluid index

Abstract

SMFM Consult Series (#46) on polyhydramnios (PH) recommends that “antenatal fetal surveillance (AFS) is not required for the sole indication of mild idiopathic” PH. A corollary is that AFS may be considered for moderate-severe (MS) PH. The objective of this study was to determine the cutoff for deepest vertical pocket (DVP) which correlates with amniotic fluid index (AFI) > 30 cm (i.e. MS PH) to guide those who utilize DVP over AFI. This retrospective study of 3rd trimester ultrasounds at 17 academically affiliated units included singletons with AFI and DVP. The study population was randomly divided into testing and validation groups. In the testing group, DVP thresholds correlating with AFI > 30 cm were calculated in two ways: i) a receiver operating curve and Youden’s J statistic (DVP-Youden) and ii) calculation of the DVP percentile that corresponded with an AFI of 30.0 (DVP-Percentile). Using the validation group, test performance was calculated for DVP-SMFM, DVP-Youden, and DVP-Percentile for diagnosis of AFI > 30 cm. From the 71,893 ultrasounds in the study period, the test group was 23,965 (33%) and the validation group 47,928 (67%). MS PH occurred in 286 (1.2%) in test group and 571 (1.2%) in validation group. An AFI of 30 cm corresponded to the 98.9 percentile and with DVP-Percentile, 10 cm. The calculated cutoff for MS PH was 8.0 for DVP-Youden (Figure). Sensitivities of DVP-Youden and DVP-Percentile were significantly higher than DVP-SMFM, but with an increased false positive rate (Table). In the sensitivity analysis, results were similar among pregnancies without diabetes or anomalies. Applying a cutoff of 8.0 cm rather than 12.0 cm increased detection of moderate-severe polyhydramnios to 100% with a false positive rate under 5%. If the SMFM DVP threshold of 12 cm were applied, 75% of the MS PH in the validation group would be missed. For obstetric practices utilizing DVP for amniotic fluid evaluation, identification of a DVP ≥ 8.0 cm should prompt further evaluation with full AFI.View Large Image Figure ViewerDownload Hi-res image Download (PPT)