Determination of gestational age measuring foetal kidneys in pregnant bitches by ultrasonography.

Abstract

The present study aimed to use foetal kidney areas as an ultrasonographic parameter to estimate the gestational age, comparing it to the widespread application of biparietal diameter (BPD) and maternal serum progesterone concentration (P4). A total of 27 clinically healthy pregnant bitches were assessed for weight, gestational age, litter size and serum progesterone levels, taking 98 complete foetal renal measurements as well as BPD from day 40 of gestation. A strong positive correlation was found between BPD and gestational age with foetal kidney area and length (p<0.005). A medium positive correlation was obtained for bitch weight and foetal kidney area and length (p<0.005) and a negative correlation was found for P4 (p<0.02). No significant association was observed between kidney area and litter size. Renal area demonstrated a 100% sensitivity and specificity at a cutoff value of 13.52 mm², making it a potentially reliable marker of fetal maturity, especially when BPD measurements are not possible. In contrast, specificity values remained low across most cut-off points between renal area and P4, limiting diagnostic usefulness of kidney measurements when used alone. However, further investigation is needed to validate predictive formulas across breeds and evaluate postnatal outcomes.