Prediction of parturition in dogs and cats : accuracy at different gestational ages

In bitches and queens, the ultrasonographic measurement of extrafoetal and foetal structures allows the evaluation of gestational age and the prediction of the parturition term for an extended period of time. The aim of this study was to investigate whether the accuracy of parturition date prediction is affected by the week of pregnancy when the ultrasonographic examination is performed. The results were obtained by retrospective analysis on the gestational period basis (from week 4 to week 9 of pregnancy) in 495 ultrasonographic examinations of pregnant bitches (small and medium size) and 60 of pregnant queens. They demonstrated that a similar accuracy (p > 0.05) was obtained by the measurement of inner chorionic cavity at week 4 and 5 of pregnancy (±1 day, 81% vs 67.7%; ±2 days, 93.1% vs 85.9%). Accuracy (±1 day) based on biparietal (BP) measurement was similar at week 5 and 6 of pregnancy (78.6% vs 78.9%; p > 0.05), whereas a significant decrease (p < 0.05) was observed at week 7 and 8 compared to week 6. No difference in the accuracy of the prediction at ±2 days based on BP was observed from week 5 to 8 of gestation (range from 82.3% to 95.2%). Close to term (week 9), the accuracies of the prediction based on BP were significantly lower than those obtained at week 5 (±1 day: 50.9% vs 78.6%, p < 0.05; ±2 days: 69.8% vs 95.2%, p < 0.005). The accuracy of the prediction in bitches and queens is influenced by the gestational period when ultrasonographic measurements are performed, particularly for BP measurement. Although a decrease in BP accuracy occurs along the pregnancy, the accuracy at ±1 and ±2 days of prediction of parturition term is highly consistent for 6 and 8 weeks of gestation, respectively.