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.

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).

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.

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.