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Deepest Pocket or AFI When Performing Prenatal Ultrasound?  


There are two sonographic techniques that are used to measure amniotic fluid for the purpose of fetal assessment: (1) the amniotic fluid index (AFI) or (2) the single deepest vertical pocket (SDP). Oligohydramnios was defined as AFI ≤ 5 cm or the absence of a pocket measuring at least 2 × 1 cm. In a population of term pregnancies and using a multicenter randomized controlled trial design, the authors found:

  • In the AFI group, there were increased cases of oligohydramnios (9.8%) compared to SDP (2.2%) as well as increased induction of labor for this particular indication (P < 0.01)
  • There were significantly more abnormal fetal heart rate (FHR) tracings in the AFI group (32.3%) compared to the SDP group (26.2%), which was more pronounced in women who were otherwise low risk (P=0.03)
  • Neither test was better at predicting adverse pregnancy outcome, including NICU admissions, and cesarean section rates
  • The use of AFI resulted in more interventions for diagnoses of oligohydramnios with no benefit, thereby making SDP the preferable approach for assessing amniotic fluid, especially in low risk women


Measuring amniotic fluid volume remains an important part of fetal assessment.  The SAFE trial (Ultrasound Obstet Gynecol, 2016), a multicentered randomized controlled trial (RCT), was designed to answer the question as to whether AFI or SDP technique is better in predicting pregnancy outcome. 1052 pregnant women at term with singleton pregnancies were included in this trial which included low risk as well as high risk indications, such as gestational diabetes (GDM), hypertensive disorder, fetal growth restriction, placental insufficiency or intrahepatic cholestasis of pregnancy.


  • AFI was associated with more women being identified with oligohydramnios, but without any significant benefit in perinatal outcome 
  • The SDP appears to be the favorable approach when estimating amniotic fluid volume in both high and low risk patients

Learn More – Primary Sources:

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.