How to measure the amniotic fluid

A. Qualitative:

  • Visual Inspection

It has been shown that the subjective estimate of the amniotic fluid volume could be as accurate as the semi-quantitative measurements (Magann et al., 1997). This technique is adequate for use during early gestation.

B. Semi-Quantitative:

  • Single Deepest Pocket (SDP)

The measurement is performed with the ultrasound probe at a right angle with the uterine wall. Measurements should exclude the umbilical cord or fetal parts. The width of each measured pocket must be at least 1 cm. Normal values range between 2-8 cm. It is also the preferred method for estimating the amniotic fluid volume in twin pregnancies.

Anhydramnion 16 ssw
This fetus at 13 weeks after spontaneous rupture of the membranes has the appearance of a fossil.

Both semi-quantitative measurement techniques correlate poorly with the actual amniotic fluid volume.

  • Amniotic Fluid Index (AFI)
The uterus is being divided into four quadrants and the deepest pocket of every quadrant is added. Normal values range between 5 and 25 cm.
Polyhydramnios 2
Single deepest pocket indicating polyhydramnios.
Studies have shown that defining oligohydramnios as a maximum vertical pocket shorter than 2 cm will result in fewer obstetric interventions without a significant difference in perinatal outcomes when compared with an AFI less than or equal to 5 cm (Nabhan AF, Abdelmoula YA, 2008).
Oligohydramnios
Single deepest pocket indicating oligohydramnios.
Bibliography
  • Magann, E. F., Perry, K. G., Chauhan, S. P., Anfanger, P. J., Whitworth, N. S. and Morrison, J. C. (1997), The accuracy of ultrasound evaluation of amniotic fluid volume in singleton pregnancies: The effect of operator experience and ultrasound interpretative technique. J. Clin. Ultrasound, 25: 249-253. doi:10.1002/(SICI)1097-0096(199706)25:5<249::AID-JCU5>3.0.CO;2-D
  • Reddy, U. M., Abuhamad, A. Z., Levine, D., & Saade, G. R. (2014). Fetal Imaging. Journal of Ultrasound in Medicine, 33(5), 745–757. https://doi.org/10.7863/ultra.33.5.745
  • 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. doi:10.1002/14651858.CD006593.pub2.

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