The significance of nonstress test from 24 to 42 weeks' gestation.

On 811 pregnant subjects, a sampling that included high-risk pregnancies, NST was performed 3,015 times from 24 to 42 weeks' gestation. Reactive NST and nonreactive NST accounted for 67.9% and 26.1%, respectively. Both amplitude and duration of acceleration showed an increase with the advance of pregnancy. The number of accelerations which occurred in the examination period increased as well. V-shaped decelerations were sometimes found in the NST recordings of normal fetuses accompanied by fetal movements, but the incidence of this type of deceleration tended to decrease as the subjects reached full term. No correlation was found between the occurrence of V-shaped deceleration during antepartum NST and that of variable deceleration during intrapartum monitoring. Taking 10 bpm and 10 seconds as the standard values of the acceleration amplitude and the duration of acceleration, respectively, there was found a significantly higher incidence of late deceleration during labor in the fetuses who showed nonreactive NST antepartally than those showed reactive NST. The incidence of persistent late deceleration was significantly higher in the nonreactive fetuses under the 10 bpm/10 second criteria than in those under the conventional 15 bpm/15 second criteria.