737: Optimal BMI for use of external fetal ECG for fetal heart rate assessment in labor

We have previously shown that in obese women, an external fetal electrocardiogram (fECG) monitoring device generates more interpretable fetal heart rate (FHR) data compared to standard external Doppler monitoring (SEM). We sought to identify the BMI cutoff where a fECG monitoring system would be preferable to SEM to optimize the amount of interpretable FHR data provided in a clinical setting. Secondary analysis of a randomized controlled trial at 4 Utah hospitals. 218 patients with singleton, term pregnancies, were enrolled at labor admission and randomized in blocks based on BMI to fECG or SEM. The proportion of interpretable 10-minute FHR tracing segments was determined following tracing evaluation by two reviewers blinded to study device allocation. A 10-minute FHR segment was deemed interpretable if tracing baseline and periodic changes could be discerned. The proportion of total interpretable minutes of FHR tracing was also evaluated. Mixed effects logistic regression models were fit to predict 10-minute and 1-minute FHR segment interpretability. Akaike information criteria (AIC) were determined to identify the optimal BMI cutoff, indicating when fECG device use consistently provides more interpretable FHR data compared to SEM. Regression model AIC plot identified BMI ≥ 31 as the ideal cut off point for fECG device performance, where fECG generated consistently more interpretable 10-minute FHR tracing segments compared to SEM (Figure 1). For the 1-minute FHR tracing analysis, an even lower BMI cut off point of 25 was identified based on AIC estimates, where fECG generated a higher proportion of interpretable minutes of FHR tracing compared to SEM at BMI 25 (Figure 2). fECG consistently generated more interpretable 10 and 1-minute FHR tracing segments compared to SEM in women with BMI > 31 and > 25, respectively. Obese women with BMI > 31 may benefit from use of the fECG device in labor.View Large Image Figure ViewerDownload Hi-res image Download (PPT)