The Effect of the Amniotic Fluid Index on the Accuracy of Ultrasonographic-Estimated Fetal Weight

Ultrasound Q. 2017 Jun;33(2):148-152. doi: 10.1097/RUQ.0000000000000275.


Background: Fetal weight estimation is one of the most important aspects of antenatal care. The effects of amniotic fluid volume on the accuracy of estimated fetal weight (EFW) depend on the amount of fluid, in particular whether it is polyhydramnios or oligohydramnios. Previous studies have reported conflicting results of the effects of amniotic fluid volume on EFW accuracy.

Aim: The aim of the study was to evaluate the effects of isolated oligohydramnios cases and polyhydramnios on the accuracy of EFW.

Materials and methods: A retrospective study was conducted at a tertiary center. The study groups consisted of 1069 term isolated oligohydramnios cases, 182 term isolated polyhydramnios cases, and 392 term-matched cases with a normal volume of amniotic fluid. Estimated fetal weight error was determined and expressed in terms of systematic error, calculated from mean percentage error and random error.

Results: The systematic error did not differ significantly between polyhydramnios and oligohydramnios cases (-3.60 [8.94%] vs -2.73 [9.7%]). The random error was 8.94% in polyhydramnios cases and 9.7% in oligohydramnios cases. The overestimation rate was 63.6% in polyhydramnios cases and 66.3% in oligohydramnios cases.

Conclusions: There were no significant differences in the accuracy of EFW between oligohydramnios and polyhydramnios. However, there was a tendency for overestimation in both types of cases.

MeSH terms

  • Amniotic Fluid / diagnostic imaging*
  • Artifacts
  • Female
  • Fetal Weight*
  • Fetus / diagnostic imaging*
  • Humans
  • Image Enhancement / methods
  • Image Interpretation, Computer-Assisted / methods*
  • Male
  • Oligohydramnios / diagnostic imaging*
  • Polyhydramnios / diagnostic imaging*
  • Pregnancy
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Ultrasonography, Prenatal / methods*