Reference values for the single deepest vertical pocket to assess the amniotic fluid volume in the second and third trimesters of pregnancy

Aim: To establish reference values for the single deepest vertical pocket to assess the amniotic fluid volume in the second and third trimesters of pregnancy. Methods: We performed a retrospective cross-sectional study with 3554 consecutive singleton low-risk pregnant women between 14 and 41 weeks of gestation. To perform the largest deepest vertical pocket measurement, the transabdominal convex probe was positioned vertical to the uterine contour of abdomen and parallel to the maternal sagittal plane. In order to obtain reference values for the largest deepest vertical pocket measurement and gestational age (GA), we have used a polynomial regression model. Results: The mean +/- standard deviation for the largest deepest vertical pocket measurement (cm) ranged from 3.1 +/- 1.1 (1.5-4.9) at 14-14+6 to 3.7 +/- 1.6 (0-6.7) at 41-41+6 weeks, respectively. A best-fit was a second-degree polynomial regression: largest deepest pocket = -1.478+ 0.197*GA-0.0030*GA(2) (R-2 = 0.014). Conclusion: Reference values for the single deepest vertical pocket to assess the amniotic fluid volume in the second and third trimesters of pregnancy in a large heterogeneous population were established.