Sampling frequency of fetal heart rate impacts the ability to predict pH and BE at birth: a retrospective multi-cohort study

Fetal heart rate (FHR) sampling rate used on the bedside is equal or less than 4 Hz. Current FHR analysis methods fail to detect incipient fetal acidemia. In a fetal sheep model of human labour we showed that FHR sampling rates near 1000 Hz are needed to detect fetal acidemia. Trans-abdominal fetal ECG (t-a fECG) sampling FHR at 900 Hz combined with a complex signals bioinformatics approach showed promise in a human cohort. Here we validate this finding in a retrospective human cohort study by comparing the performance of the same bioinformatics approach to predict pH and BE at birth in the cohorts with FHR sampled either at 4 Hz or at 900 Hz. The 4 Hz FHR recording data sets consisted of the open access intrapartum CTG data base with n = 552 subjects used to develop the predictive model and another cohort of prospectively recruited n = 11 labouring women to then validate it. 900 Hz FHR data set comprised two prospectively recruited t-a fECG cohorts of n = 60 and n = 23 subjects. Recruitment criteria were similar across the cohorts. We have determined the goodness of fit (R-2) and root mean square error (RMSE) as the performance indicators of the model on each cohort. The clinical characteristics of all cohorts were similar (gestational age 280 +/- 8 d; gender 50% male; birth body weight 3.5 +/- 0.5 kg; pH and BE at birth 7.25 +/- 0.1 and -5.7 +/- 3.4 mmol L-1, respectively; 1' and 5' Apgar scores at birth 8.5 +/- 1.4 and 9.4 +/- 0.6, respectively). The 4 Hz FHR cohort rendered-for pH and BE-R-2 = 0.26 and 0.2 and RMSE = 0.087 and 3.44, respectively. This could not be confirmed in the validation cohort for neither pH nor BE prediction. The 900 Hz FHR cohort rendered-for pH and BE-R-2 = 0.9 and 0.77 and RMSE = 0.03 and 1.70, respectively, and the pH prediction was validated. In our model, lower FHR sampling rate increased the predicted error range similar to 3-4 fold. We show that increasing FHR sampling rate to 900 Hz improves prediction of fetal pH and BE at birth. This should improve early identification of babies at risk of brain injury.