Direct volume measurement at midtrimester amnioinfusion in relation to ultrasonographic indexes of amniotic fluid volume.

Abstract

Our purpose was to investigate the relationship between amniotic fluid volume and semiquantitative ultrasonographic assessment of amniotic fluid in the midtrimester. Sixteen pregnancies between 16 and 28 weeks with minimal amniotic fluid (severe oligohydramnios or anhydramnios) and intact membranes were studied at the time of clinically indicated amnioinfusion. The amniotic fluid index and deepest pool measurement were determined before and immediately after the procedure. Correlations were sought by means of standard regression techniques with amniotic fluid volume (i.e., volume infused) on the basis of the assumption that amniotic fluid volume before amnioinfusion was effectively nil. There was a significant linear relationship between amniotic fluid index and volume infused (y = 7.336 + 0.015x; R2 = 0.30, p < 0.05). However, no correlation with the deepest pool measurement technique was found (R2 = 0.11, p > 0.05). Amniotic fluid index is preferable to deepest pool measurement in assessing amniotic fluid volume in the second trimester of pregnancy. The low variance (30%) suggests that better predictors of amniotic fluid volume are still required.