Introduction

Radiography and ultrasonography are both widespread methods used in veterinary obstetrics. In a ventrodorsal radiographic view, measurements of fetal biparietal or head diameter (HD) and maternal pelvic diameter are commonly used to predict the risk of dystocia in dogs and cats due to relatively oversized fetus. However, HD measurement is easier to perform with ultrasound scan.

Objectives

To compare and find the correlations of fetal HD measured by radiography and ultrasonography in dogs and cats.

Methods

Twenty-seven dogs and seventeen cats were diagnosed in last trimester of pregnancy at Kasetsart University Veterinary Teaching Hospital during 2017–2018. Fetal HD was measured by radiography and transabdominal ultrasonography on the same day. The correlations between the two techniques and linear regressions of HD were statistically analyzed.

Results

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 were significant (r=0.85 in dogs and r=0.94 in cats, p<0.0001). Linear regression formulas were y=1.0716x+0.1661 (R²=0.72) in dogs, and y=0.9627x+0.3148 (R²=0.88) in cats (y=HD by radiography, x=HD by ultrasonography).

Conclusions

Fetal HD measurements were different between two modalities. The formulas above can be implied to estimate relatively oversized fetus.