Monitoring of pregnant women before delivery routinely includes the nonstress test (NST), which often is used in early pregnancy. The investigators sought to determine whether maternal position during the NST at different stages of pregnancy influences fetal heart rate (FHR) patterns. The 368 women included in the study, who had a total of 1055 NSTs, each lasting 30 minutes, were in a reclining or sitting position or walked during the NST. Telemetry was used to record the test in those who walked. Parameters considered were minutes of reactive NST with minimum length, number of fetal movements, baseline FHR, number of large accelerations, number of dubious NST, and number of variable decelerations.
The reclining position did not substantially influence the duration of NST, but in the sitting position or during walking, the time needed to record three large accelerations of a reactive tracing decreased significantly as pregnancy progressed. Mothers perceived more fetal movements when reclining. Baseline FHR did not vary significantly with maternal position but declined as pregnancy progressed. Gestational age and maternal position did not significantly influence the number of large accelerations. Dubious NST results became less frequent in all groups as pregnancy continued. The highest rates, observed before 37 weeks gestation, were 7.6% while walking, 6.1% while reclining, and 5% while sitting. After 39 weeks, variable decelerations of FHR were most numerous in the reclining position followed by the sitting position and least numerous while walking.
These observations suggest that two factors influence the NST: gestational age and maternal position during the test. Testing in the sitting position or during walking should be encouraged because FHR reactivity is observed most rapidly under these circumstances.