Doppler indices of the equine fetal carotid artery throughout gestation

Assessment of pregnancy viability in the equine patient is currently based on gestational profiles of limited prognostic value. In recent years Doppler technology has been applied to uterine and umbilical arteries of pregnant mares to monitor fetal responsive haemodynamics, suggestive of compromise. To date, uterine artery Doppler indices failed to provide sufficient evidence of pregnancy viability and the umbilical cord of the equine fetus is inconsistently visualized past 250 days gestation. The objectives of this study were to: i) evaluate intracranial blood flow impedance by Doppler examination of the fetal carotid artery and ii) establish reference values for healthy, uncomplicated pregnancies. The middle cerebral artery (MCA), a branch of the carotid artery, is commonly employed to assess intracranial hemodynamics in the human fetus, exhibiting high resistance to circulation to the fetal brain in uncomplicated pregnancies. For the purpose of this study, 12 pregnant mares were examined at 2–3 weeks interval by B mode and Doppler ultrasonography until delivery and a novel technique was developed for Doppler evaluation of the carotid artery in the equine fetus, in order to provide objective evidence of the hemodynamic status of the equine fetus. Additional biophysical and biochemical parameters were collected to demonstrate appropriate pregnancy development. In this study Doppler waveform analysis of fetal intracranial vasculature demonstrated an elevated blood flow impedance, showing a significant correlation of carotid Doppler indices with gestational age. Results were comparable to human fetal trends for the middle cerebral artery (MCA) from mid gestation to term. Biochemical data showed expected patterns of uncomplicated pregnancies. •Current tools available to assess equine pregnancy viability show poor predictive value for pregnancy outcome.•Doppler studies of the uterine arteries demonstrate poor predictive value to rule out adverse pregnancy events.•The umbilical cord is inconsistently visualized for Doppler assessment, past 250days gestation.•The present study proposes a novel technique for assessment of fetal intracranial circulation, by Doppler interrogation of the carotid artery.•Equine fetal carotid Doppler indices show high vascular impedance and a statistically significant correlation with gestation.•The findings are in agreement with the human literature for the Doppler indices of fetal MCA.