APPROXIMATE ENTROPY OF FETAL HEART-RATE IN NORMAL AND GROWTH-RETARDEDFETUSES

Objective: To compare approximate entropy values of fetal heart rate o btained in normal and growth retarded fetuses and to assess the diagno stic efficacy of this measurement in predicting fetal acidosis in comp arison with standard measurement of fetal heart rate. Methods: We cons idered 210 recordings obtained cross sectionally in uncomplicated sing leton pregnancies at 28 to 42 weeks of gestation and 45 recordings obt ained immediately before elective cesarean section in growth-retarded fetuses secondary to uteroplacental insufficiency, Fetal heart rate wa s recorded for 60 min and 11 different parameters were analyzed by mea ns of a commercially available computerized system, Approximate entrop y was calculated using sequential epochs of 2.5 sec with a window leng th (m) of 2 epochs and a filtering level (r) of 2 bpm, Acidosis at bir th was considered when umbilical artery pH was below 7.210, a value co rresponding at the lower 95th limit of our confidence limit constructe d on normally grown fetuses undergoing elective cesarean section. Resu lts: Approximate entropy linearly increases in normal fetuses with adv ancing gestation. Stepwise regression evidenced that the number of lar ge accelerations, short term variability, and delta values were indepe ndently related with approximate entropy (multiple r = 0.823). In grow th-retarded fetuses lower approximate entropy values were evidenced wi th respect to normal fetuses and these differences are particularly ev ident in fetuses acidotic at birth. Of all the fetal heart rate parame ters tested, approximate entropy values show the higher diagnostic eff iciency in predicting acidosis in growth-retarded fetuses. Conclusion: Approximate entropy was a better indicator of acidosis at birth than the conventional measurements of fetal heart rate.