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

Abstract

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 (R² = 0.73) in
dogs and y = 0.96x+0.30 (R² = 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.