Single formulae of inner diameter of chorionic cavity and biparietal diameter for the prediction of parturition term in different size bitches of non-brachycephalic breeds

The enormous variety in size among different canine breeds, prompted the elaboration of size-specific formulae of ultrasonographic fetal biometry to accurately identify gestational age (GA) and to predict the parturition 1. Among different parameters, the inner diameter of chorionic cavity (ICC) and the biparietal diameter (BP) provided a highly accurate prediction in small, medium, large and giant size dogs1-3. However, the availability of one single formula for ICC or BP of all different size dogs would simplify the everyday use of fetal biometry in clinical practice. The aims of this retrospective analysis were 1) to derive a single growth curve of ICC and BP for all size bitches of non-brachycephalic breeds; 2) to evaluate their accuracy for parturition term prediction. A total of 67 measurements of ICC and 111 of BP (using SonoAce 8800, Medison Co. Ltd., Seoul, Korea) of 32 bitches, equally divided in 4 different sizes, were analyzed by a multiple linear regression model to investigate the relationship between ICC or BP growth, maternal body weight (MBW) and GA. The accuracy of the prediction obtained with 166 ICC and 367 BP of non-brachycephalic bitches of different sizes, was compared to that obtained with the size-specific formulae2,3. A significant relationship between GA, MBW and ICC or BP was obtained (p<0.001) and the derived equations were as follows: ICC y=(z-66.3384-0.1767*x)/1.5121 (r2=0.97); BP y=(z-26.9346-0.0488*x)/0.693 (r2=0.97) where z=measurement of ICC or BP (mm), x=MBW (kg), y= GA (days before parturition), a=intercept, b and c=regression coefficient. The accuracies (±1 day and ±2 days) of ICC and BP obtained with the single formula were not statistically different from those obtained with the size-specific formulae. The high accuracy suggests the use of these formulae in routine application of fetal biometry for parturition term prediction in non-brachycephalic breeds. The growth curves of ultrasonographic parameters in brachycephalic bitches, prone to feto-pelvic disproportion, deserve further studies. [1] Luvoni GC, Beccaglia M. The prediction of parturition date in canine pregnancy. Reprod Domest Anim 2006;41:27-32. [2] Luvoni G.C., Grioni A. Determination of gestational age in medium and small size bitches using ultrasonographic foetal measurements. J Small Anim Pract 2000;41:292-4. [3] Alonge S, Beccaglia M, Melandri M, et al. Prediction of parturition term in large and giant size bitches by ultrasonographic measurements. Proc.18th EVSSAR Congr, Hannover, Germany,2015;p145.