Background: Doppler ultrasonography is increasingly used to assess fetal circulation in canine pregnancy, but
reference information for small-breed dogs during late gestation remains limited.
Objective: To describe preliminary Doppler hemodynamic measurements of the umbilical artery and vein and selected major fetal arteries in healthy small-breed dogs during late gestation, and to explore associations
between vascular indices and fetal left ventricular systolic measurements.
Methods: Twenty clinically healthy pregnant bitches weighing <10 kg and examined during gestational weeks
6-8 were included in this cross-sectional study. Gestational age was estimated ultrasonographically from fetal biparietal diameter. Color and pulsed-wave Doppler ultrasonography were used to evaluate the umbilical artery and vein and the fetal abdominal aorta, iliac artery, and carotid artery. Left ventricular dimensions and wall
thicknesses were obtained by M-mode echocardiography, and fractional shortening (FS) and ejection fraction (EF) were calculated. Data were summarized descriptively. Exploratory associations were assessed using Spearman rank correlation because several variables were non-normally distributed.
Results: Mean maternal age was 2.10 ± 0.52 years, estimated gestational age was 51.50 ± 7.54 days, and mean litter size was 4.19 ± 2.11 fetuses. Mean umbilical artery resistive index (RI), pulsatility index (PI), and
maximum velocity were 0.81 ± 0.18, 1.56 ± 0.55, and 30.87 ± 11.83, respectively. Mean fetal abdominal aortic
RI and PI were 0.82 ± 0.08 and 1.65 ± 0.46. Mean EF and FS were 91.91 ± 5.94% and 62.84 ± 12.75%, respectively. Umbilical artery RI and PI were positively associated with iliac arterial resistance indices, whereas FS was negatively associated with umbilical artery PI. EF and FS were strongly correlated, as expected from their mathematical and physiological interdependence.
Conclusions: This study provides preliminary descriptive Doppler data for umbilical and fetal arterial circulation in healthy late-gestation small-breed dogs. The findings support the feasibility of combined fetal vascular Doppler and M-mode assessment; however, larger longitudinal studies with outcome data and repeatability analysis are required before population reference intervals or clinical decision thresholds can be established.