Sequential nonstress testing with use of each fetus as its own control.

The sequential nonstress tests of 126 high-risk fetuses were assessed for baseline fetal heart rate, acceleration frequency, amplitude, and duration and the observance of fetal heart rate decelerations. In 108 fetuses (563 tests) with normal perinatal outcomes, no significant trends in these parameters were found. In 18 fetuses (104 tests) with perinatal compromise, 16 had significantly declining acceleration frequencies, 15 had decreasing acceleration duration, four had rising mean baseline rates, and seven, in their last test before delivery, had repetitive late or severe variable decelerations. The last tests of 11 of these 18 fetuses met institutional criteria for reactivity. When the nonstress tests of compromised fetuses were viewed sequentially, acceleration frequency declined by an average of 59% and acceleration duration by an average of 40%. Sequential assessment of the nonstress test, when compared with the use of standard reactivity criteria, improved test sensitivity from 39% to 89% and negative predictive value from 91% to 98%. We conclude that sequential nonstress test assessment in individual fetuses may improve the diagnostic value of this modality and lead to earlier recognition of fetal compromise.