Final answer:
Hysterosonography is best performed during the proliferative phase of the menstrual cycle, which extends from approximately day 7 to 14.
Step-by-step explanation:
Hysterosonography, also known as a saline infusion sonogram, is usually performed during the proliferative phase of the menstrual cycle. The proliferative phase normally ranges from around day 7 to 14. During this time, the endometrium is regenerating and is typically at a stage that is well-suited for the procedure, with minimized risk of disrupting any potential early pregnancy and as well as providing a clear image before the secretions that mark the later secretory phase. The goal of hysterosonography is often to evaluate the uterine cavity, and doing this before ovulation in the proliferative phase allows for optimal visualization.