STANDARDS FOR THE QUANTIFICATION OF SERIAL CHANGES IN THE AMNIOTIC-FLUID INDEX

A total of 274 low-risk pregnancies underwent predetermined scheduled serial ultrasound examinations nod measurements of the amniotic fluid index (AFI). As expected from previous cross-sectional studies, there is a gradual decline in the AFI from mid-trimester until term. The lon gitudinal nature of this data set permits the construction of conditio nal centiles for AFI whereby the AFI of an individual fetus at a given gestational age can be extrapolated to give a range of expected value s for AFI (expressed as centiles) at a Inter gestational age. Examples of conditional centiles based upon 4-week measurement separations are presented. These conditional centiles permit the appropriate evaluati on and quantification of time-dependent changes in AFI to be made.