Moderate-to-Severe Polyhydramnios Cutoffs for Deepest Vertical Pocket Corresponding to Amniotic Fluid Index

Objective Society for Maternal-fetal medicine Consult Series (#46) states "antenatal fetal surveillance is not required for mild idiopathic" polyhydramnios defined as amniotic fluid index (AFI) of 24 cm or a deepest vertical pocket (DVP) between 8 and 11 cm. The objective of this study was to determine the cutoff for DVP which correlates with AFI >= 30 cm. Methods This retrospective study of singleton third trimester ultrasounds included a study group randomly divided into test and validation. In the test group, DVP cutoffs correlating with AFI >= 30 cm which was used to define moderate-severe polyhydramnios were calculated in two ways, rounded to the nearest whole number: 1) a receiver operating curve and Youden's J statistic (DVP-Youden) and 2) calculation of the DVP percentile that corresponded with AFI of 30 cm (DVP-Percentile). Using the validation group, diagnostic characteristics were DVP-Youden and DVP-Percentile for diagnosis of AFI >= 30 cm and were compared against SMFM cutoffs (DVP-SMFM). Results Seventy one thousand eight hundred and ninety three ultrasound exams in the 3rd trimester had assessment of AFI and DVP. Moderate-severe polyhydramnios occurred in 286 (1.2%) in test group and 571 (1.2%) in validation group. AFI of 30 cm corresponded to the 98.9th percentile, which in turn correlated to a DVP of 10 cm (DVP-Percentile). The calculated cutoff for moderate-severe polyhydramnios was 8 cm for DVP-Youden. Conclusion Using 8.0 cm rather than 12.0 cm increased the detection of moderate-severe polyhydramnios to 100% with a false positive rate under 5%. For those utilizing DVP for amniotic fluid evaluation, identification of a DVP >= 8.0 cm should prompt further evaluation with complete AFI.