Amniotic Fluid Index Versus Single Deepest Vertical Pocket as a Screening Test for Preventing Adverse Pregnancy Outcome

A Cochrane review [Abstract] 1 included 5 studies with a total of 3 226 women with singleton pregnancies. There were no difference between amniotic fluid index (AFI) and single deepest vertical pocket (SDP) in the prevention of poor peripartum outcomes, including admission to a neonatal intensive care unit (RR 1.04, 95% CI 0.85 to 1.26; 5 trials, n=3 226); an umbilical artery pH of less than 7.1; the presence of meconium; an Apgar score of less than 7 at five minutes; or caesarean delivery. However, with AFI significantly more cases of oligohydramnios were diagnosed (RR 2.39, 95% CI 1.73 to 3.28; I² =59%), and more women had inductions of labor (RR 1.92, 95% CI 1.50 to 2.46) and caesarean delivery for fetal distress (RR 1.46, 95% CI 1.08 to 1.96).

A multicenter randomized controlled trial 2 included 1052 pregnant women with a term singleton pregnancy. Women were assigned randomly to AFI or SDP measurement for estimation of amniotic fluid volume. Oligohydramnios was defined as AFI ≤ 5 cm or the absence of a pocket measuring at least 2 × 1 cm. The diagnosis of oligohydramnios was followed by labor induction. Postpartum admission to a neonatal intensive care unit was similar between groups (4.2% [n = 21] vs 5.0% [n = 25]; RR 0.85, 95% CI 0.48 to1.50). In the AFI group, there were more cases of oligohydramnios (9.8% [n = 49] vs 2.2% [n = 11]; RR 4.51, 95% CI 2.2 to 8.57; P < 0.01) and more cases of labor induction for oligohydramnios (12.7% [n = 33] vs 3.6% [n = 10]; RR 3.50, 95% CI 1.76 to 6.96; P < 0.01) than in the SDP group. Moreover, an abnormal cardiotocography was seen more often in the AFI group than in the SDP group (32.3% [n = 161] vs 26.2% [n = 132]; RR 1.23, 95% CI 1.02 to 1.50; P = 0.03). The other outcome measures were not significantly different between the two groups.

A study 3 reanalyzed ultrasound estimates in identifying oligohydramnios, normal fluid, and polyhydramnios using normal volumes calculated by quantile regression (QR). The overall level of agreement for the AFI was fair, and that for the SDP was slight. Although not statistically significant, the positive predictive value to classify a low volume using the AFI was lower compared to the SDP (35% vs 43%). The positive predictive value for a high volume was higher using the AFI compared to the SDP (55% versus 31%) but not statistically significant. Both the AFI and SDP identified actual normal AFVs by QR, with sensitivity higher than 90%. The SDP was superior for identification of oligohydramnios, and the AFI superior for identification of polyhydramnios.

Comment: The quality of evidence is downgraded by imprecise results (few outcome events).

References

• Nabhan AF, Abdelmoula YA. Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome. Cochrane Database Syst Rev 2008;(3):CD006593 [Review content assessed as up-to-date: 30 April 2009]. [PubMed]
• Kehl S, Schelkle A, Thomas A et al. Single deepest vertical pocket or amniotic fluid index as evaluation test for predicting adverse pregnancy outcome (SAFE trial): a multicenter, open-label, randomized controlled trial. Ultrasound Obstet Gynecol 2016;47(6):674-9. [PubMed]
• Hughes DS, Magann EF, Whittington JR, et al. Accuracy of the Ultrasound Estimate of the Amniotic Fluid Volume (Amniotic Fluid Index and Single Deepest Pocket) to Identify Actual Low, Normal, and High Amniotic Fluid Volumes as Determined by Quantile Regression. J Ultrasound Med 2020;39(2):373-378 [PubMed]