Consistent temo rise before O dip?

This more an I'm-curious question, as I've miscarried twice, clearly in can get pregnant, but I've noticed a typical pattern in my cycle that seems not typical for most. My temp drops slowly half awy through AF, stays low, spikes the day before 0, dips the day of, then slowly rises and stays there until half way through AF. I know that slow rising and O day dips are normal, but what's with the spike just before? Here's a really clear example of it:

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and another..

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Sometimes the spike lasts 1-2 days, sometimes it spikes then gradually drops over the next day or two, but there seems to always be that spike. What could cause that?

It's totally normal. your body builds the lining in the early days of the cycle (even when you're on AF!) and then once things are good in that dept. it takes kind of a "day off" to save up its raw materials so it can make a big bunch of estrogen for the surge. :)