Percent Acceleration Time

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Abstract
The percent acceleration time (PAT) is a fetal heart rate parameter, which may be derived from the nonstress test (NST). It is based on measurement of the duration of individual movement-associated fetal heart rate accelerations (MAFAs), obtained during a nonstress test, and is calculated by the formula: PAT = [total MAFA duration (second)]/[total NST duration (second)] .times. 100. The authors studied 148 fetuses undergoing four or more serial nonstress tests who were delivered within one week of their last test. Percent accleration time of fetuses with normal outcomes had a mean value of 15.5 .+-. 10.0 (SD)%, correlated well with the frequency and amplitude of movement-associated fetal heart rate accelerations but was independent of gestational age and mean baseline fetal heart rate. No normal fetus had a percent acceleration time of less than 5% on its last nonstress test, while only one abnormal fetus had a percent accederation time that exceeded the mean percent acceleration time of the normal group. All abnormal fetuses had a significant progressive decline in percent acceleration time (mean: 50.6%). Percent accleration time values were more sensitive in identifying fetuses with perinatal compromise then were conventional criteria for nonstress test reactivity, and may provide a useful alternative to assessment of fetus status when other quantitative methods are unavailable (continuous ultrasound visualization) or less reliable (maternal perception, tokodynamometry, palpation).

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