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 a rtificial rupture of membranes and whether this acute loss of fluid vo lume affected umbilical artery resistance as measured by Doppler veloc imetry. Twenty-five uncomplicated term pregnancies underwent umbilical artery velocimetry and amniotic fluid index determination in the acti ve phase of labor before and after amniotomy. Amniotic fluid loss was measured by direct collection of fluid during and immediately followin g rupture of the membranes. The preamniotomy and postamniotomy data we re compared using the paired t test, and the relationship between amni otic fluid index change and actual fluid loss was tested by linear reg ression. The change in the amniotic fluid index after amniotomy was si gnificant (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 signi ficant changes in the amniotic fluid index, however, no significant ch ange in the umbilical artery systolic/diastolic ratio could be demonst rated. 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 meth od of assessing acute changes in amniotic fluid volume.