Estimated Placental Volume
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Information for Providers
EPV can be measured from 7 to 40 weeks. Use widest angle probe for large placentas. Beyond 36 weeks the placenta may be too large to visualize the entire width.
Ideal measurements: Freeze a perpendicular cross section at the maximal width of placenta. Take Width measurements from edge to edge. Start at apex and measure Height and Thickness down to baseline along same line (at right angles to Width line). Height is always greater or equal to thickness.
To download the simple two-page manual click here
EPV is calculated from three ultrasound measurements
Steps to perform an EPV
If the placenta is an obvious crescent, find the maximum width while holding the probe perpendicular to the placenta surface. Start with the baseline Width measurement by creating a line from one tip of the placenta to the other, as shown by the (+) yellow line.
Find the maximal apex point of the crescent, place a point for a second line at this apex. The Height is measured by dragging the line from the apex to baseline (⸭), yellow line, making sure the Height line is perpendicular when it touches the Width line.
The Thickness is measured by starting from same apex point as Height and then measuring along the same line down to edge of placenta (✕), orange line.
If the placenta is flat, without any evidence of curvature, the above steps will not work. This most often happens with early first trimester placentas. In this case, first determine the maximal Width by measuring from tip to tip (yellow). The Height and Thickness lines (orange) are the same and are measured once to obtain both values. Simply plug the W, H and T values into the calculator and the correct EPV will be outputted.
Correct and incorrect placenta cross sections
Sweep through the placenta until you find the maximum cross section. If the umbilical cord is centrally inserted, this can serve as a guide to both find the maximum cross section and help to maintain the probe perpendicular to the placental surface. The widest probe angle is desirable, with adjustments to depth of penetration to visualize the entire placental cross section as necessary.
Proper probe angles during EPV scan
Keep the probe perpendicular to the surface of the placenta, without regard to the angle of the probe to the patient’s skin. Do not take an image that is oblique through the placenta as this will lead to an erroneously large thickness reading. Do not press too firmly on the patient’s abdomen as that might distort the placental shape. The final image you freeze should be crisp along the entire length of the placenta. Placentas overlying the cervical os or that are totally fundal may be difficult to image.
iOS and Android EPV apps
EPV Normative Curves for manual percentile calculations
Find the iPhone Merwin's EPV Calculator here.
Find the Mac Desktop calculator here.
Find the Android calculator here.