Introduction:

The C-HEALTH study investigates how environmental and socio-economic conditions affect women's menstrual cycles and reproductive health.

Aim:

To compare progesterone levels during the luteal phase among women from different socio-economic backgrounds living in rural and urban areas in southern France.

Methods:

This is a prospective observational study involving 320 healthy women of reproductive age.

• Hormones (progesterone, estradiol) will be measured daily in saliva.
• Inflammation (Protéine C Réactive: CRP) will be measured five times per cycle via blood drops.
• Participants will wear a smart ring to monitor body temperature and activity.
• Daily symptoms and lifestyle data will be collected.
• Environmental exposures (pollution, stress, living conditions) will be assessed and linked to menstrual health outcomes.

Introduction:

Menstrual health is an important indicator of women's overall health, but the biological and environmental factors influencing the menstrual cycle are still poorly understood. The C-HEALTH study explores how social and ecological conditions - such as pollution, stress, socio-economic status, and living environment - affect hormonal patterns and menstrual health in women living in the Occitanie region (France).

Aim:

The primary objective is to compare luteal phase progesterone levels among women from different socio-economic backgrounds living in either rural or urban areas in the Occitanie region.

The secondary objectives are:

• To compare, according to the women's environment: levels of sex hormones (progesterone and estradiol) throughout a menstrual cycle, levels of an inflammation marker (C-reactive protein) throughout a menstrual cycle, and the description of the menstrual cycle (characteristics, possible abnormalities such as pain, abnormal bleeding, etc.).
• To identify environmental factors associated with potential biological and menstrual cycle abnormalities.

Methods:

To meet the objectives of this research, 80 women aged 18-45 living in Occitanie (France) will be enrolled in each socioeconomic group at each location (4 groups: low-income urban, high-income urban, low-income rural, high-income rural; total n=320).

After the inclusion visit (visit 1) and the training visit for self-sampling (visit 2), participants will collect their biological samples and data during one observed menstrual cycle, with a follow-up visit on day 7 of the cycle (visit 3), and will complete their participation with the collection of biological samples at home (visit 4).

Biological samples (saliva and dried blood spots) will be collected no later than 30 days after the end of the collection period.

The exposome matrix will be inferred using postcode and will include data from an air pollution database (Environment Data Management System - EDMS) linked primarily to traffic, industry, stationary fuel burners, forest fires and solid fuel combustion, comfort parameters (temperature, humidity), UV, pollen count, green, grey and blue spaces, vegetation, Shannon biodiversity index, noise, water quality (pesticides, heavy metals)

At the end of this study:

• Saliva samples will be analyzed using ELISA tests to measure steroid levels.
• Dried blood spot samples will be analyzed using immunoenzymatic assays to measure CRP levels, using the ELISA technique.
• The exposome will be analyzed using classical statistics, clustering/PCA (Principal Component Analysis) to assess exposure profiles, and EnWAS will be used to untangle independent associations between exposure variables and menstrual cycle parameters. A series of minimally adjusted univariate analyses will be performed and exposures significant at the false discovery rate will be retained in the cluster analysis. Within each cluster, a multivariable analysis will be performed to reduce the number of variables of interest. This will allow us to identify exposome factors independently associated with menstrual health.

Inclusion Criteria:

• Woman of childbearing age (18-39 years)
• Woman not using hormonal contraception for at least 6 months
• Woman with semi-regular menstrual cycles between 21 and 45 days inclusive
• Woman with no known history of infertility
• Woman working in the same environment (urban/rural) as her place of residence
• Knowledge of the dates of periods over the last 3 cycles
• Woman who has a freezer at -20°C

Exclusion Criteria:

• Diagnosis by a physician of one or more of the following comorbidities: Polycystic ovarian syndrome (PCOS), Endometriosis, Adenomyosis, Diabetes or thyroid disease, Hormone-dependent gynecological cancers (breast, endometrium, ovaries), Coagulation diseases (von Willebrand), Chronic liver failure, chronic renal failure, heart disease, autoimmune disease, Autism, Diagnosis and/or treatment for a psychiatric illness
• Chronic exposure to cocaine, amphetamine/methamphetamine, morphine or ecstasy within 30 days prior to inclusion
• Chronic exposure to THC within 7 days prior to inclusion.
• Person who is not comfortable with self-sampling (hematophobia or other)
• No access to a smartphone
• No possibility of wearing a connected ring for at least 60 days 22h/24h
• Pregnant or breastfeeding woman
• Woman who gave birth or breastfed in the 2 months before the study
• Person who moved less than 2 years before the study (does not concern participants who moved in the same environment (rural or urban, less than 20 km)
• Person unable to read French
• Failure to obtain informed consent
• Person not benefiting from a national health insurance scheme
• Person under legal protection, guardianship or curatorship
• Person participating in other research involving the human person

Women were initially recruted from medical and paramedical practices, hospitals, clinics, pharmacies and medical advisors from the different environments studied in Occitanie, then in a second time via social networks (Facebook and Snapchat) and local newspapers (e.g. Midi Libre) in the event of recruitment difficulties.

De-identified individual participant data (IPD) will be made available to other researchers upon reasonable request, following publication of the main study results. Data sharing will be subject to approval by the study steering committee and may require a data-sharing agreement to ensure compliance with GDPR and ethical guidelines

• Start Date: 6 months after publication of primary results
• End Date: 5 years after data availability begins

Qualified researchers with a scientifically and ethically sound proposal will be eligible to access the de-identified individual participant data (IPD) and supporting documents, including the study protocol, statistical analysis plan, informed consent form, and analytic code