I’ll confess I haven’t put much thought into this, but Kelly Schmidt has. She has type 1 diabetes and has to deal with it. Kelly writes:
“Some woman will use a higher basal [insulin dose] the week before and during a period, where others need less insulin as blood sugars plummet upon a period. Take notes each month, even if you just insert a few sentences in your calendar. We all say we will remember next month, but trust me, these notes will be handy. A quick example of how I use 2 basals: my normal, non-period basal is just shy of 10 units, and then my PMS basal is 11.5 units of Humalog. As you can see, I just need a pinch more of insulin, but it’s so helpful.
Know that with every month, the fluctuations and impact a period has on someone not only varies with the person, but can vary from month to month.”
Paleo Diabetic 