Effect of progesterone receptor antagonists on the resistive index of the umbilical artery and foetal heart rate variations in whelping induction protocols

This study assessed foetal heart rate (FHR) variations and umbilical artery resistive index (RI) as indicators of parturition timing in dogs undergoing induced whelping using two progesterone receptor antagonists, aglepristone and mifepristone. Sixteen pregnant bitches were divided into two groups receiving either aglepristone or mifepristone. Doppler ultrasonography showed that an FHR variation over 15 per cent, combined with an umbilical artery RI below 0.7 in the caudal foetus, predicted imminent whelping within 24 h. A higher RI above 0.75, 24 h after induction, was linked to dystocia and necessitated a caesarean section. Both aglepristone and mifepristone induced late-gestation changes similar to normal whelping signs, including FHR accelerations and decelerations, increased FHR variability, and decreased umbilical artery RI, with no significant difference between the two protocols. Monitoring FHR patterns and umbilical artery RI together provides a non-invasive and reliable method for predicting delivery timing and assisting with timely interventions during induced whelping; however, larger studies with more comprehensive neonatal outcomes are needed for validation.