What is the accuracy of the ultrasonographic fetal measures in the prediction of parturition in mesaticephalic and brachycephalic cats

Background: Ultrasound is commonly used in queens for diagnosis and monitoring of pregnancy and may also be used to estimate the date of birth in cats with unknown date of mating, representing a valuable aid in clinical practice and in reproductive programs. The determination of gestational age can be made based on sonographic fetal measurements. In bitches, the conformation of the cranium should be considered in proportional variations in measurements because it interferes with predicting parturition date. Although domestic cats do not show a large variation in terms of size, they present variation in the cranial conformation. So far, there is no study that has produced mathematical equations for determination of gestational age in cats considering these differences. Thus, there is a widespread use of these equations that can lead to mistakes in this estimation. This study aimed to verify the accuracy of prediction of delivery date in cats of different cranial conformation through mathematical equations enshrined in clinical practice, using different sonographic measurements and verify the effect of litter size on the accuracy of determination of days to delivery. Materials, Methods & Results: Sonographic examinations were performed on pregnant brachycephalic and mesaticephalic cats. Biparietal and abdominal diameters and depth of the fetal diencephalo-telencephalic vesicle were measured. The average value of each structure was calculated and ultrasound prediction of days before delivery was obtained by applying equations derived from growth curves that have been already published. All mathematical equations used in predicting the date for delivery showed lower percentage of success, regardless of the type of the parameter and cranial ultrasound used. The biparietal diameter was the most reliable measure for estimating the date of delivery. The litter size did not infl uence the accuracy of determining the date of delivery. Discussion: Although queens have ovulation induced by copulation and date of birth would be more easily predicted than in bitches, with a good accuracy and subsequent birth date, it is extremely important to be able to plan clinical delivery assistance or a c-section. In this study, the application of the equations derived from the growth curves of biparietal and abdominal diameter and depth of the fetal diencephalo-telencephalic vesicle resulted in little accurate predictions of delivery date for the three and sonographic parameters for both types cranial. The generalization use of these equations for cats may lead to errors in the estimation of gestational age. Although the equations used in this study are old, we opted for their use in this work, because they are still widely used in ultrasound practice, still being cited in recent publications on this subject. Studies that performed the ultrasound monitoring of pregnancy in cats and dogs show that the fetus ordinary course follows a well-defi ned development with particular characteristics of development at specifi c times during pregnancy. This makes clear that the evaluation of these characteristics is useful for predicting the day of delivery and can also be applied in other breeds, unlike the mathematical equations that are specifi c to each breed standard. Thus, it is suggested that the estimate of gestational age is made in conjunction with the fetometry and observation of fetal growth and subsequent organogenesis, avoiding the use of one of the tools individually so that one has higher reliability in this prediction. Thus, it was concluded that the mathematical equations already published are not individually suffi cient for accurate determination of date of birth in brachycephalic and mesaticephalic cats.