Will menstruation change my results?

The recommendation is to always scan in the same phase of the menstrual cycle

It is important to maintain consistency around scanning throughout the Menstrual Cycle as there are significant fluid changes around hormonal shifts.  As you can see in the diagram, during the luteal phase, progesterone rises which has a natural diuretic effect.  Whereas, in the follicular phase, estrogen rises which can increase fluid retention significantly.  The recommendation is to always scan in the same phase of the menstrual cycle ie. in the follicular or luteal Phase, within the same few days.