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The 4-vessel Sampling Approach to Integrative Studies of Human Placental Physiology In Vivo
Published on: August 2, 2017
Amniotic fluid index versus maximum vertical pocket for predicting adverse perinatal outcomes in singleton term
Manal Massalha1,2, Gharid Nourallah Bekdache1, Bryon DeFrance1
1Department of Obstetrics and Gynecology, McMaster University, Hamilton, Canada.
Objective:
Amniotic fluid assessment is central to antepartum fetal surveillance. Current guidelines favor the maximum vertical pocket (MVP) over the amniotic fluid index (AFI), as AFI increases oligohydramnios diagnosis and labor induction rates without improving perinatal outcomes. Neither method accurately identifies true oligohydramnios by dye-dilution techniques (sensitivity 6-30%), and the clinical significance of AFI-detected oligohydramnios unconfirmed by MVP remains uncertain. We aimed to compare the diagnostic accuracy of AFI versus MVP for predicting adverse perinatal outcomes in singleton term pregnancies, with attention to discordant classifications.
Methods:
Retrospective cohort study of 671 singleton pregnancies delivered at term (≥37 weeks) at a tertiary center (2017-2024). All patients underwent antepartum ultrasound within 7 days of delivery. Oligohydramnios was defined as AFI <5 cm or MVP <2 cm. The primary composite outcome included cesarean delivery for nonreassuring fetal heart rate, 5-min Apgar score <7, umbilical artery pH <7.10, or meconium-stained fluid requiring neonatal airway intervention within 30 min of birth.
Results:
The composite outcome occurred in 124 pregnancies (18.5%). AFI identified oligohydramnios in 141 cases (21.0%) versus 55 for MVP (8.2%, P < 0.0001). AFI showed higher sensitivity (26.6% vs. 10.5%) but lower specificity (80.3% vs. 92.3%). Positive predictive value and negative predictive value were similar between methods. Among 91 pregnancies with AFI-only oligohydramnios, adverse outcome rates (22.0%) fell between concordant normal (17.3%) and concordant oligohydramnios (26.0%), although differences were nonsignificant. AFI oligohydramnios was not independently associated with adverse outcomes (adjusted odds ratio, 1.28 (95% confidence interval, 0.80-2.05). Sensitivity differences were most pronounced in small-for-gestational-age pregnancies (AFI 45.1% vs. MVP 28.9%, P for interaction = 0.047).
Conclusion:
AFI classified more pregnancies as oligohydramnios than MVP, but AFI-only oligohydramnios was not associated with significantly worse outcomes in this MVP-guided cohort. Both methods showed limited discriminatory performance, and these findings should not be interpreted as grounds to modify current guideline recommendations.
