Guides series, Life Stages and T1D
The Menstrual Cycle and Type 1 Diabetes
Three weeks of the cycle, things mostly behave. Then the seven days before the period arrive and the same lunch you have eaten for years runs to 14 mmol/L (252 mg/dL) when last week it would have stayed under 9 mmol/L (162 mg/dL). The pattern is real, the data has caught up, and the conversation is finally getting somewhere.
Ask Grace
Want to ask whether the cycle pattern fits your own data? Ask Grace.
Why this guide exists
In the DAFNE and BERTIE courses, women keep raising the same arc. Three weeks when things mostly behave. Then a week when the same meal pulls a glucose curve they have not seen for the previous twenty days. For decades the literature could not match that recognition with the right size of evidence. In the last four years it has caught up.
Real-world flash CGM cohorts of hundreds of women, AID-era secondary analyses, and a PRISMA-compliant systematic review (Gamarra and Trimboli 2023, Journal of Personalized Medicine) have arrived together. The pattern is clear at the population level: forty to sixty per cent of women with T1D notice a measurable cycle-driven glucose change, the luteal phase is where most of the signal lives, AID systems shift the work without erasing it, and the wider hormonal life course (contraception, PCOS, pregnancy, menopause) intersects with T1D at every station.
Individual variation is real. The population pattern does not predict any one woman’s; the data tells you whether the pattern is signal in your own cycles when you overlay it.
How to read this guide
Each part stands on its own and links back to the others. Read in order if the topic is new; jump to the part that fits your question if you already know the cycle pattern in your own data.
Part 1: What the body is doing
The four phases of the cycle, the glucose pattern in each, the heterogeneity of who sees it clearly and who does not, and the conversation script for taking your data to the diabetes care team. Anchored to Tatulashvili 2022, Brown 2015, Gamarra and Trimboli 2023, and the GNL Syno cycle dataset.
Open Part 1Part 2: AID systems across the cycle
What CamAPS FX, Tandem Control-IQ, Tandem Mobi (CIQ+), MiniMed 780G, and Omnipod 5 have been measured to do across the cycle, the AID Algorithm Optimiser ladder reviewed by but not endorsed by the manufacturer global medical leads (Grade D educational synthesis on a Grade A/B evidence base), and the named-system conversation with your diabetes care team. Anchored to Levy 2022, Monroy 2025, Mesa 2024, and AiDAPT.
Open Part 2Part 3: Contraception, PCOS, Pregnancy, Menopause
The four hormonal life-course stations where T1D and the wider arc meet most directly. Hormonal versus non-hormonal contraception (Visser 2013 Cochrane); PCOS prevalence and screening (Codner 2007, Teede 2023); pregnancy planning, antenatal care, and intrapartum management (NICE NG3, JBDS-IP 12, NPID Audit 2023, CONCEPTT, AiDAPT, HAPO); menopause and T1D, the most under-served station (Courtney 2025, Slopien 2018 EMAS).
Open Part 3Who this is for, and what it is not
This guide is for adult women living with T1D, the partners and family supporting them, and the clinicians who want a contemporary read. The age scope is adult and older-adult; the menarche transition for T1D girls is covered in the Paediatric T1D guide.
The guide is educational. It explains population-average patterns and gives you the language to ask. It does not give doses, it does not personalise correction, and it is not a substitute for the conversation with your diabetes care team. The numbers your team gives you, on your data, in your context, are the ones that count.
The body talks back honestly through the glucose. The cycle is one of the rhythms it talks in, and this guide translates the rhythm with recognition rather than as a results table.