Effect of fetal heart rate on umbilical arterial Doppler indices

Umbilical arterial Doppler indices (UaDI) are recognized as potentially useful tools for fetal surveillance. However, elucidation of the diagnostic reliability of UaDI requires further analysis of the factors that affect the variance of the indices. This prospective study was undertaken to analyze the effects of one such factor, the fetal heart rate (FHR). The study population consisted of 194 cases of uncomplicated pregnancy with normal outcome, with the gestational age (GA) ranging from 27 to 39 weeks. A continuous wave Doppler instrument with a 4-MHz transducer was used. The UaDI measured were diastolic/average (D/A) ratio, systolic/diastolic (S/D) ratio, pulsatility index (PI), and resistance index (RI). Linear regression of the data grouped in 2 week GA intervals demonstrated a moderate but statistically significant (p less than .05) correlation between FHR and UaDI. The influence of FHR on UaDI was then further analyzed by multiple regression technique using GA as the second independent variable. The regression demonstrated that 15% to 18% of the total UaDI variance was attributable to FHR effect. Moreover, when UaDI data were standardized for a FHR of 140 beats per minute and GA of 34 weeks using a multiple regression-based equation, the 95% limits of the UaDI were reduced by 32%, 34%, 26%, and 32% for D/A, S/D, PI, and RI, respectively. This study demonstrates a statistically significant effect of FHR on UaDI. However, clinical significance of this observation requires further investigation.