Multifactorial monitoring of pregnancy in the canine species: embryonic resorptions, resistivity index, and serum concentration of vitamins

Monitoring the pregnancy in the bitch is important in order to increase the possibility of positive maternal and fetal outcomes. Ultrasonographic pregnancy diagnosis at around 25 days post-ovulation allows to detect the embryos, their viability and the presence of resorption sites. Embryonic resorptions are a common phenomenon in polytocous species but in the present study they seem to be more common than previously thought (present in 48.3% of pregnancies compared to 4.8-12.3% described in the literature) and more frequent in older bitches. Resorption sites are also related to an impaired uterine blood flow at pregnancy diagnosis. In the present study, uterine artery resistivity index (RI) increases as the proportion of resorptions within a single pregnancy increases. The underlying mechanisms of this relationship are unknown, but in other species an altered uterine blood flow results in pregnancy loss and other gestational pathologies. In both studies, the most part of the resorptions did not involve other conceptuses, with the continuation of pregnancy and no physical signs shown by the mother. These findings suggest that spontaneous embryonic resorptions could be due both to physiological causes, such as uterine overcrowding for large litters, and to unknown pathological mechanisms, linked to ageing. Among the possible causes of pregnancy failure, vitamin deficiencies are reported to be one of them. Vitamin deficiencies in several species have been correlated with other negative pregnancy outcomes, such as altered fetal growth and low birth weight neonates. From the analyses done in the present study, no major alterations of vitamin levels seem to happen from the heat-stage until day 45 of pregnancy in bitches fed commercial maintenance diets. Further studies are needed to determine reference values for each vitamin during the different phases of pregnancy, including the last ones, to evaluate the prevalence of deficiencies in the canine species and to plan appropriate interventions if necessary.