Maternal position during non-stress test and fetal heart rate patterns

Objective.  The aim of the study was to determinate whether maternal position during the non-stress test (NST) in different weeks of pregnancy influences fetal heart rate patterns. Materials and methods.  A total of 1055 NST lasting 30 min were performed in 368 autochthonous mothers with low-risk pregnancies. On the basis of maternal position during the test we divided into three groups: reclining, sitting, and walking. The cardiotocographic parameters considered were: number of minutes of reactive NST with minimum length, number of fetal movements, fetal heart rate baseline, number of large accelerations, number of dubious NST, and number of variable decelerations. Results.  Fetal heart rate patterns in low-risk pregnancies were studied using NST in different gestational ages and in different maternal positions. Differences in heart rate were found in relationship to both gestational age and maternal position. The minimum length of NST necessary to record at least three large accelerations was significantly different in relationship to both gestational age and maternal position. The number of fetal movements perceived by the mother was greater in the reclining position than in sitting or walking. Together with the progression of pregnancy, the number of dubious NST decreased in all subgroups, especially in the sitting position. The greatest number of variable decelerations was observed in the reclining position and it was increased with pregnancy progression. The NST duration did not vary greatly in the reclining position, but in the sitting position or during walking, the time taken to record the three large accelerations required to define the trace as reactive, decreased significantly with the progression of pregnancy Conclusions.  Non-stress test in sitting position or during walking should be encouraged because fetal reactivity is more quickly observed.