Clinical evaluation of the accuracy of foetal radiographic findings in parturition date prediction of small size dogs

Abstract

Ultrasonographic measurements of extra-foetal or foetal structures have been reported as an accurate means of
predicting the date of parturition in the bitch. However, for many years, radiography has been clinically useful for
pregnancy diagnosis, determining the number of foetuses and prolonged foetal death. Guidelines for estimating the
canine parturition date based on foetal skeletal mineralization in relation to gestational age and preovulatory LH surge
have been applied in small animal practice. The aims of this retrospective study were to evaluate the accuracy of
parturition date prediction using foetal radiographic findings in small size dogs (1-10 kg), and to determine factors
affecting the accuracy of predicting. Bitches of different breeds were submitted for pregnancy diagnosis using a
computed radiography system, and images (both ventrodorsal and lateral views) were evaluated by two radiology
specialists. The retrospective study involved pregnancies of 92 small size bitches showing natural onset of parturition.
Prediction of parturition date was made according to the guideline previously published; days before parturition (DBP)
was calculated based on pregnancy length of 65 days. Only 11.9% (11/92) whelped on the prediction date. Parturition
mostly occurred before the prediction date (3.4 ± 2.5 days, range 1-11) in 64 out of 92 bitches (69.6%), and 18.5% (17/92)
of bitches whelped after the predicted date (2.2 ± 1.5 days, range 1-5). The accuracy rates when predicting the delivery
day within ±1 day, ±2 days and ±3 days were 36.9% (34/92), 56.5% (52/92) and 66.3% (61/92), respectively. In this
study, the factor affecting the accuracy of parturition prediction was gestational age (r=0.27, P=0.008). Close to term
(64-65 days of pregnancy), the accuracy of parturition prediction was significantly lower than those obtained during
48-63 days (P<0.01). Maternal age (P=0.09), body weight (P=0.4) and litter size (P=0.88) did not affect the prediction
accuracy. In conclusion, the canine parturition date was predictable using radiographic identification of foetal bony
structures with low accuracy. Because the minority (11.9%) whelped on the prediction date and most of pregnant
bitches (69.6%) whelped before predicted parturition date, the accuracy is not acceptable to time planned caesarean
section.