Correlation of measured amniotic fluid volume and sonographic predictions of oligohydramnios

Objective: To compare the measured volume of amniotic fluid (AF) in term gestations to the volume predicted sonographically. Methods: One hour before elective cesarean delivery, 40 women had sonographic measurement of the AF index and largest vertical pocket diameter. At surgery, a suction catheter was placed into a 1-cm uterine incision and a second catheter was used to aspirate AF from the operative field. Hemoglobin concentration was measured in the collected AF to determine the extent of blood contamination. Results: The mean measured AF volume was 532 mL (range 40–1692). The correlation coefficient between AF index and AF volume was 0.744 (P < .001). A similar value (r = 0.755, P < .001) was observed for the largest vertical pocket measured with ultrasound. Conclusion: Sonographic measurements of the largest vertical pocket and the AF index have similar positive correlations with measured AF volumes at term. Current methods of estimating AF volume have low sensitivity for detecting oligohydramnios.