Feto-maternal heart rate ratio in pregnant bitches : effect of gestational age and maternal size

Few information is available on parameters that can be used to objectively assess the foetal health during canine pregnancy. To identify a reliable parameter for the evaluation of foetal well-being, the effect of pre-gestational maternal bodyweight and gestational age on foetal heart rate (FHR) and on feto-maternal heart rate ratio (FHR/MHR) was investigated. Seventeen client-owned pregnant bitches of different pre-gestational maternal bodyweight were examined by serial echo colour Doppler. Only data from 11 uncomplicated pregnancies were included in the statistical analysis. The relationship between FHR, and FHR/MHR, and independent variables was analysed by polynomial regression (p ≤ .05). The FHR and the FHR/MHR significantly fitted a multiple quadratic regression for all independent variables. They both increased from 35 to 20 days before parturition and then a decreasing pattern followed. Higher values of both parameters were observed in bitches of lowest and highest bodyweight. Patterns of FHR and FHR/MHR were similar, but the ratio better describes the effect of the independent variables on the data. Thus, the highest significance of FHR/MHR compared to FHR alone encourages the application of this ratio to evaluate foetal well-being. The equation derived by the regression analysis of FHR/MHR could be applied in clinical practice to obtain its expected values in healthy pregnancies.