Approximate entropy of fetal heart rate variability as a predictor of fetal distress in women at term pregnancy

Background. The aim of this study is to investigate the relationship between approximate entropy (ApEn) of fetal heart rate (FHR) with umbilical blood gas parameters and the power spectrum of FHR variability in Chinese and to test whether ApEn of FHR variability could be used as a predictor of fetal distress in women at term pregnancy. Methods. Sixty-seven pregnant women with singleton, term fetus were recruited for the recording of FHR variability and the data were used for the estimate of ApEn. Blood gases after birth were measured through umbilical artery. Results. In all 67 neonates, there was some amount of interinfant variability in the ApEn values with a mean of 1.139 +/- 0.169. The ApEn values were significantly (P < 0.05) correlated with pO(2), SO2, pCO(2), pH, HCO3, or base excess (BE). The 15 fetuses with low ApEn (ApEn < 1.0) had higher risk of metabolic acidosis (BE less than -12 mmol/l) than those with high ApEn (ApEn >= 1) (likelihood ratio = 12.301, P < 0.001). The powers of FHR variability in all frequency ranges (0-0.256 Hz) were lower in the low-ApEn group than those in the high-ApEn group. Conclusions. The ApEn of FHR variability significantly decreased during fetal asphyxia, including hypoxia, hypercapnia, and both respiratory and metabolic acidosis; low ApEn was linked to decreased power spectrum density in all frequency domains. The ApEn values may be used as a predictor of fetal distress in women at term pregnancy.