Fetal pulse oximetry and wavelet analysis of the fetal heart rate in the evaluation of abnormal cardiotocography tracings.

AIM: Previous studies indicate that the addition of wavelet analysis of the fetal pulse oximetry tracings (FSPO2) and fetal heart rate (FHR) variability to cardiotocography (CTG), for intrapartum fetal monitoring, provides useful information on the fetal response to hypoxia. We applied the new procedure in non-reassuring CTG patterns, in which cesarean section was performed, and tested its accuracy in the diagnosis of the intrapartum fetal compromise.

METHODS: At the 'Aretaieion' University Hospital labor ward, 318 women with term fetuses in the cephalic presentation entered the trial during labor. They all were monitored with external CTG and fetal pulse oximetry. In the cases that cesarean section was applied, because of abnormal CTG tracings, we applied a method based on the multiresolution wavelet analysis and a self-organized map neural network on the first and second stage of labor. The main outcome parameter was the rate of cord metabolic acidosis at birth (pH < 7.05). Secondary outcomes included Apgar scores at 5 min, fetal transmission to neonatal intensive care unit (NICU) and neonatal encephalopathy.

RESULTS: Fifty out of 318 cases delivered operatively because of abnormal CTG patterns (rate 15.72%). In 30 cases, cord pH was >7.05, while in 11 Apgar scores at 5 min were <7, while none of those neonates were transferred to NICU. In the rest 20 cases cord pH was <7.05; in all of these cases Apgar scores at 5 min were <7, while four neonates were transferred to NICU. In one of them, neonatal encephalopathy was diagnosed. After the offline application of wavelet analysis and neural networks to the pulse oximetry and FHR variability readings of the 50 cases, statistics calculated that the system showed a sensitivity of 85% and a specificity of 93%, while false negative and false positive rates were 15% and 7%, respectively.

CONCLUSION: Computerized FHR and FSPO2 monitoring shows an excellent efficacy and reliability in interpreting non-reassuring FHR recordings.