In 77 menstruating adults with type 1 diabetes contributing 380 cycles on automated insulin delivery, insulin requirements and glucose varied systematically by cycle phase. Total daily dose and carbohydrate intake peaked in the luteal phase, alongside higher mean glucose and less time in range, and modelled insulin sensitivity was about 2.6% higher in the early follicular phase than the mid-luteal.
The clinic use is to ask before adjusting. A patient reporting a week of unexplained highs each month is describing physiology, not a lapse in technique, and current algorithms do not account for it. Ask where the highs fall in the cycle before changing a ratio, and consider phase-specific settings where the system allows. Around one in six participants did not follow the population pattern, so confirm it in the individual rather than assuming it.
- Insulin needs and glucose rise in the luteal phase, even on automated delivery
- Modelled insulin sensitivity about 2.6% higher early follicular than mid-luteal
- Ask where in the cycle the highs fall before changing settings
- About 15% do not follow the pattern, so confirm it individually
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