The distribution of accelerations of the human fetal heart rate at 38 to 40 weeks' gestational age.

In order to further understand the use of antepartum fetal heart rate monitoring we measured the distribution, in time, of two, three, or five fetal heart rate accelerations of greater than or equal to 15 bpm for greater than or equal to 15 seconds and of greater than or equal to 10 bpm for greater than or equal to 6 seconds in 12 healthy pregnant women at 38 to 40 weeks' gestation. The length of time necessary to measure 50% or 95% of intervals containing five accelerations would be substantially reduced by changing to a definition of two or three accelerations. However, an observation interval of at least 80 minutes is required to include the longest time interval of two, three, or five accelerations. These data may suggest new strategies for decreasing time and expense of fetal heart rate testing.