Fetal Head Diameter in Dogs and Cats Measured by Radiography and Ultrasonography

In abdominal radiography, the measurement of fetal biparietal diameter or head diameter (HD) and maternal pelvic diameter are commonly used to predict risk of dystocia due to relatively oversized fetus. Besides fetal viability, fetal head measurement is also easy to perform with ultrasound. However, fetal HD measured from both techniques has never been compared. The objectives of the study were to compare and to find the correlations of fetal HD measured by both techniques at the last trimester of pregnancy in dogs and cats. Twenty four dogs and sixteen cats diagnosed for near-term parturition at Emergency Surgery Unit, Kasetsart University Veterinary Teaching Hospital during the period 2017-2018 were included in the study. Fetal HD was measured by both techniques on the same day. The correlations between the two techniques and linear regressions of HD were statistically analyzed. Radiographic measurements of fetal HD were larger than those measured by ultrasonography in both dogs (p<0.0001) and cats (p<0.0001). The correlations between the results of skull heads from abdominal radiographs and ultrasonogram were significantly correlated (r = 0.73 in dogs and r = 0.94 in cats, p<0.0001). Linear regression formulas were y = 1.08x+0.13 (R-2 = 0.73) in dogs and y = 0.96x+0.30 (R-2 = 0.88) in cats (y = HD by radiography and x = HD by ultrasonography). In conclusion, the formulas above can be used to estimate fetal HD between radiography and ultrasonography.