Acute amniotic fluid loss and changes in the amniotic fluid index : correlation and effect on umbilical artery velocimetry

This study was undertaken to determine whether changes in the amniotic fluid index accurately reflected measured amniotic fluid loss after artificial rupture of membranes and whether this acute loss of fluid volume affected umbilical artery resistance as measured by Doppler velocimetry. Twenty-five uncomplicated term pregnancies underwent umbilical artery velocimetry and amniotic fluid index determination in the active phase of labor before and after amniotomy. Amniotic fluid loss was measured by direct collection of fluid during and immediately following rupture of the membranes. The preamniotomy and postamniotomy data were compared using the paired t test, and the relationship between amniotic fluid index change and actual fluid loss was tested by linear regression. The change in the amniotic fluid index after amniotomy was significant (paired t test, P < .0001), and a significant relationship was found by linear regression between the actual amniotic fluid loss and the change in the amniotic fluid index (P < .01, r2 = .28). Despite significant changes in the amniotic fluid index, however, no significant change in the umbilical artery systolic/diastolic ratio could be demonstrated. Our data suggest that amniotomy in the active phase of labor in uncomplicated pregnancies does not affect umbilical artery resistance and that the amniotic fluid index is a limited, semiquantitative method of assessing acute changes in amniotic fluid volume.