(675) Deepest vertical pocket with reflex amniotic fluid index as a screening approach for polyhydramnios

Friday, January 31, 2025

10:30 AM – 12:30 PM

Submitting Author and Presenting Author(s)

Alexandra JD Phelps, MD (she/her/hers)

Maternal-Fetal Medicine Fellow
Vanderbilt University Medical Center
Nashville, Tennessee, United States

Coauthor(s)

Amelie Pham, MD (she/her/hers)

Assistant Professor
Vanderbilt University Medical Center
Nashville, Tennessee, United States
NR

Niharika Ravichandran, MD

Resident Physician
Vanderbilt University Medical Center
Nashville, Tennessee, United States
MG

Matthew Grace, MD

Vanderbilt University Medical Center
Nashville, Tennessee, United States
TM

Trey McGonigle, MS

Vanderbilt University Medical Center
Nashville, Tennessee, United States
SH

Shi Huang, PhD

Vanderbilt University Medical Center
Nashville, Tennessee, United States
Aleksandra Polic, MD

Assistant Professor
University of Pittsburgh Medical Center
CP

Catherine Phillips, MD

Vanderbilt University Medical Center
Nashville, Tennessee, United States
Lisa C. Zuckerwise, MD (she/her/hers)

Associate Professor
University of Virginia Health
Charlottesville, Virginia, United States

Objective: To describe concordance between amniotic fluid index (AFI) and deepest vertical pocket (DVP) in the assessment of amniotic fluid volume and to determine the utility of using DVP alone as a screening test for clinically significant polyhydramnios.

Study Design: We performed a retrospective cohort study of all outpatient ultrasounds (US) performed at 20.0-41.6 weeks gestation at an academic institution from 2018-2022. Measurements from the US most proximate to delivery were used to analyze the occurrence of polyhydramnios, defined by DVP (≥ 8cm) or AFI (≥ 24cm). We classified severity using accepted definitions by each methodology. Tests of diagnostic performance were calculated using AFI as the accepted gold standard. Pearson correlation coefficient was calculated to describe the relationship between DVP and AFI.

Results:

Measurements from 11,688 US met inclusion criteria. Polyhydramnios was diagnosed in 739 (6.3%) US using AFI and 875 (7.5%) using DVP. Using DVP of ≥ 8cm as a cutoff identified all cases of moderate or severe polyhydramnios by AFI (Table). However, it also indicated polyhydramnios in 337 cases where AFI was normal, a false positive rate of 3.1%. Of 193 patients with moderate or severe polyhydramnios by AFI, 171 (88.6%) were misclassified as mild by DVP. Using DVP as a screening tool to identify moderate or severe polyhydramnios yielded sensitivity of 100% (95% CI 98.1-100%), specificity of 94.1% (95% CI 93.6-94.5%), positive predictive value of 53.1% (95% CI 51.3-54.9%), and negative predictive value of 100% (95% CI 99.9-100%). DVP and AFI were highly correlated (Figure, r=0.84, p < 0.01).

Conclusion: Using DVP as a screening tool, with reflex measurement of AFI if DVP is ≥ 8cm, is predicted to identify all cases of moderate or severe polyhydramnios and reduce over-diagnosis of mild polyhydramnios both in cases of normal AFI and in those with more significant polyhydramnios.