The pathogenic variant does not change over time but in VWD there is significant expressivity...
What can women do to prepare for lab testing/getting lab work to ensure we get test results? Should we not do lab testing immediately before or after menses? Are there foods we should avoid?
It is possible that in the first few days of a woman's cycle the VWF levels are lowest, but this probably is only important in those with very mild disease--those with levels that straddle between normal and low. Foods have not been shown to make a difference in testing results, even those that may have anti-platelet properties. So the bottom line is the levels are probably not that much different between the first few days of the menstrual cycle compared to the middle or end of the cycle and probably not different in on a low dose estrogen pill or COC (not on a multiple times a day estrogen containing pill).
Although not definitively proven, my experience is that when a patient is very anemic (low red blood cells, low iron) the VWF levels tend to be a bit higher so I often defer testing until the anemia is under better control. It is definitely known that if the body is under significant medical stress the VWF levels and FVIII levels will be high. For example, I would delay testing if you have a bad cold, the flu, or an ear infection as the VWF levels may not be at its steady state.