Characteristics of long-range monitoring of fetal heart rate in third trimester with atypical non-stress test

Abstract

Objective To analyze the characteristics of long-range monitoring of fetal heart rate in the third trimester fetuses with atypical non-stress test (NST). Methods Long-range monitoring of fetal heart rate was performed in low-risk pregnant women who received antenatal care between April 2014 and October 2015 in Peking University Third Hospital. All subjects underwent NST from the 36th gestational week, and divided into normal NST (30 cases) and atypical NST (36 cases) groups according to the results of NST. The clinical data, including maternal age, gestational age at delivery, termination of pregnancy, neonatal asphyxia, hospitalization rate and umbilical cord blood peak-systolic/diastolic ratio value were collected. The data of long-range monitoring were analyzed by specially designed computer software. T test and Chi-square test were applied for statistical analysis. Results There were no differences in maternal age, gestational age at delivery, mode of delivery and incidence of neonatal asphyxia between the two groups (all P>0.05). In atypical NST group, fetal heart rate baseline was higher [(138.05±5.65) vs (135.10±5.39) bpm] (t=-2.170, P<0.05), and fetal heart rate baseline variability was lower than in normal NST group [(5.19±1.07) vs (6.28±1.15) bpm] (t=3.960, P<0.001). Compared with normal NSTs, the percentage of mild baseline variability was significantly increased in atypical NST group [(40.79±9.97) vs (51.17±10.84)%], while that of moderate variability was significantly decreased [(56.57±8.86) vs (46.72±10.24)%] (t=-4.018 and 4.133, both P<0.001). In atypical NSTs, the average ratio of time of acceleration/the whole time of monitoring [(37.41±4.60)%] and acceleration area per unit time[(1.42±0.48) cm2/20 min] were decreased compared with normal NSTs [(40.78±4.23)% and (2.03±0.67) cm2/20 min] (t=3.079 and 4.359, both P<0.05). Conclusions Long-range monitoring of fetal heart rate in the third trimester fetuses with atypical NST is characterized by the declined fetal heart rate baseline variability, increased proportion of mild variability and unit time acceleration area; but these are not associated with pregnancy outcomes and short-term prognosis. Key words: Fetal monitoring; Heart rate, fetal; Pregnancy trimester, third; Electrocardiography