RESUMO
To introduce approximate entropy (ApEn) in the analysis of fetal heart rate variability (FHRV) and to discuss the relationship between the ApEn values and perinatal outcomes, 67 computerized cardiotocographs were recorded. Approximate entropy and index in time domain were used to analyze FHRV. After childbirth, the neonatal Apgar scores were recorded and umbilical cord arterial blood gas analyses were performed. The results showed the ApEn values of FHRV were correlated with pH, Pco2, Po2, HCO3-, ABE, SO2 and neonatal Apgar scores (r = 0.51, -0.29, 0.49, 0.29, 0.45, 0.56, 0.28, respectively, P < 0.05). The ApEn values for acidotic fetuses (pH less than 7.20) were significantly different from those of normal fetuses (P < 0.01), however the time domain parameters of FHRV were unable to identify the difference. The results suggest that the ApEn values of FHRV are closely related to the fetal hypoxia and acidemia. Thus the ApEn analysis appears to be useful for improving the sensitivity in the diagnosis of fetal distress.