Doppler waveform of dectus venosus in canine fetuses : correlation with neonatal mortality

Background: The Doppler ultrasonographic evaluation of the ductus venous (DV) blood flow has not been described in dogs yet. The evaluation of DV blood flow is considered in human medicine an important indicator of fetal well being. 
Purpose: The present study aims to define if the Doppler ultrasonographic morphology of DV waveform can predict neonatal mortality in dogs. 

Methods: Forty-six clinically healthy pregnant bitches underwent ultrasonographic evaluation (B-mode and Doppler technique) with a 7,5-13 MHz linear transducer). The bitch with the lowest gestational age was 36 days pregnant and the one with the highest was 66 days pregnant. Two fetuses for each pregnancy (except in case of singleton) were considered: the most cranially and the most caudally into the uterus. The well-being of the canine fetus was checked ultrasonographically evaluating the fetal movements and heart beat. The DV appears as a short trumpet-shaped vessel with a sparkling appearance, arising from the umbilical vein and entering the caudal vena cava. A sequence of at least three successive and symmetric waves was acquired using pulsed-wave Doppler. Waveforms were classified as diphasic or threephasic. Odds ratios (OR) were calculated with 95% confidence intervals (CI), to compare the chance of neonatal mortality in litters with one or more DV threephasic waveforms with litters without threephasic waveforms. 

Findings: Eighty-one of the 191 fetuses were evaluated. Neonatal mortality (death during the first 6 hours after birth) recorded was 10 %. Eighteen fetuses belonged to litters with neonatal mortality, in which threephasic waveform was observed in pregnancy. Six fetuses belonged to litters without neonatal mortality, in which threephasic waveform was observed in pregnancy. Forty-nine fetuses belonged to litters without neonatal mortality, in which only diphasic waveform was observed in pregnancy. Eight fetuses belonged to litters with neonatal mortality, in which only diphasic waveform was observed in pregnancy. The correlation between the presence of a threephasic waveform and neonatal mortality was significant (OR, 18.38; 95% CI, 5.6-60.3, p<0,0001). Considering only singleton or twin fetuses, 100% of fetuses were evaluated (27 fetuses from 19 bitches). Two out of these 27 fetuses presented both threephasic waveform and neonatal mortality; the remaining 25 showed diphasic waveform without neonatal mortality. The correlation between the presence of a threephasic waveform and neonatal mortality was significant (OR, 255.00; 95% CI, 4.10-15849.21, p=0.0085). 
Conclusion: The evaluation of the DV during pregnancy to detect the presence of a threephasic waveform could be used to predict neonatal mortality in dogs. Our results appear to be very similar to those reported in human medicine, but further studies are needed. No conflict of interest statement: yes Ethical statement: No ethical approval was obtained, not required.