Pyometra generally occurs between 9–12 weeks after estrus when the uterus is under progesterone influence from an active corpus luteum. The sonogram shows a dilated, fluid-filled uterus typical of pyometra. | Pyometra generally occurs between 9–12 weeks after estrus when the uterus is under progesterone influence from an active corpus luteum. The sonogram shows a dilated, fluid-filled uterus typical of pyometra. |