This study aims to examine how ovarian hormone fluctuations across the menstrual cycle affect sleep patterns. Using objective sleep tracking, hormone phase assessment, and validated questionnaires, it will assess changes in sleep quality, duration, menstrual symptoms, sleepiness, chronotype, anxiety, and depression over one full cycle.

Study design:

A prospective community-based study focusing on women of reproductive age (18-36 years) designed to evaluate whether the phase of the menstrual cycle affects sleep quality and/or sleep duration. The study methods and results will be reported following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) for cross-sectional studies.

Recruitment of Participants:

If approved by the local research ethics committee (VSN-2411037), the study will be registered at ClinicalTrials.gov and women of reproductive age (18-36 years) will be recruited. The main method of recruitment will be a message sent through social media messaging system. Women residing in Iceland will be invited to participate. All the women participating in the study will be provided with information about the study and asked to sign a written informed consent before entering the study. All participants will be allowed to withdraw from the study at any time. Participants will not be financially compensated for their participation.

General Health & Sleep Evaluation (subjective):

Before starting the program, women that have signed an informed consent to participate will attend an introductory meeting (approximately 30 minutes), for women not living in Akureyri and neighbourhood but want to participate in the study meeting will be held virtually. Women still interested to participate after the meeting be asked to fill out questionnaires to evaluate:

1. Demographics and general health.
2. The impact of menstrual distress and its impact on psychological well-being. The Menstrual Distress Questionnaire (MEDI-Q) is a twenty-five-item questionnaire with reliability of 0.84 and score >=20 indicating menstruation-related distress.
3. Level of daytime sleepiness. The Epworth sleepiness scale (ESS), is an eight-item questionnaire with reliability 0.73 and score of 11-15 indicating mild-moderate sleepiness and >=16 severe sleepiness.
4. Nighttime and daytime components of insomnia. The Insomnia severity index (ISI), is a seven-item questionnaire with reliability 0.83 and score of 15-21 indicating mild-moderate and >=22 severe insomnia symptoms.
5. Severity of anxiety. The General anxiety disorder-7 scale (GAD-7), a seven-item questionnaire with reliability 0.91 and score of 10-14 indicating mild-moderate and >=15 severe anxiety symptoms.
6. Severity of depression. The Beck's depression inventory-II (BDI-II), is a ten-item questionnaire with reliability 0.90 and score of 20-28 indicating moderate and >=29 severe depression symptoms.
7. Preferred timing of sleep and activity. The Morningness-Eveningness questionnaire (MEQ), is a nineteen-item questionnaire with reliability 0.68 and scores of 16-41 indicating evening type, 42-58 intermediate type and 59-86 morning type.
8. Preferred food choices.

Menstrual Cycle Tracking:

Ovulation days will be detected using a commercial urine test for luteinizing hormone (LH) (PREGMATE, Ovulation Midstream Test Predictor Kit; sensitivity level:25mlU/mL). Participants will be instructed to use ovulation tests, starting 5 days before the expected ovulation (day 10) and for the next 7-10 days or until the first the first positive results are detected notify the study co-ordinator and share a photo of the results. Then participants will be asked to continue using the ovulation test for 3 more days.

Sleep Evaluation (Objective):

Participants will asked to record their sleep for all nights over period of one-menstrual cycle (starting the first day of their period and ending when the next period starts) with FDA_cleared_182618 home sleep test (HST) (SleepImage System; MyCardio LLC, Denver, Colorado, US). This test also complies with the EU Medical Device Regulation (CE mark 2862).

The SleepImage System comprises a finger-worn data-collection device including a photoplethysmography sensor (PPG) and a mobile application that sends the data to a secure cloud-based portal for data analysis (Figure 1). The data-recorder collects plethysmography-signal (PLETH) and oxygen saturation (SpO2) information that is automatically analyzed utilizing cardiopulmonary-coupling (CPC) algorithms to derive sleep information, then combined with SpO2 to calculate apnea hypopnea index (AHI). The CPC-method has been described in detail in several prior publications. In brief, the method is based on recording and analyzing dynamics in signals controlled by the autonomic nervous system (ANS) during sleep, more specifically by calculating the coherence between heart/pulse rate variability and respiratory excursions derived from a PLETH-signal. Then, a spectral analysis is performed to generate sleep stages. Non-rapid eye movement (NREM) sleep is presented as bimodal: stable sleep (high-frequency coupling, HFC;0.1-0.5Hz) that includes all electro-encephalogram (EEG) estimated NREM-3 and part of NREM-2 sleep, and is associated with periods of stable breathing, non-cyclic alternating pattern (CAP) EEG, increased delta power and blood pressure dipping and unstable-sleep (low-frequency coupling, LFC;0.01-0.1Hz) that includes all NREM-1 and portion of NREM-2 associated with sleep instability, characterized by variability of tidal volumes, blood pressure non-dipping and CAP-EEG. Wake and rapid eye movement (REM) sleep show very low-frequency coupling characteristics (vLFC;0-0.01Hz). The output includes sleep onset (SO), sleep conclusion (SC), sleep duration, total sleep time (TST), wake after sleep onset (WASO), sleep efficiency (SE), sleep quality index (SQI) displayed on a scale of 0-100, and AHI.

Investigators have in a previous study confirmed the feasibility to use this method for multi-night testing.

Inclusion Criteria:

1. Women, 18-36 years
2. Body Mass Index (BMI) <=35
3. Regular menstrual cycle, defined as: length of menstrual cycle 22-35 days and length of menses <10 days.
4. Women with natural menstrual cycle (i.e., do not use any type of hormonal contraceptives) and women using contraceptives (comparison group).

Exclusion Criteria:

Previously diagnosed with:

1. Sleep apnea, clinical insomnia, restless leg syndrome, narcolepsy.
2. Shift work and trans-meridian travel during the study period.
3. Chronic atrial fibrillation or ventricular trigemini, severe uncontrolled asthma, or other pulmonary diseases.
4. Premenstrual Dysphoric Disorder (PMDD) or severe Premenstrual Syndrome (PMS).
5. Other severe medical conditions that may affect cerebral metabolism, cancer, diabetes, rheumatoid arthritis, or other chronic health conditions.
6. Severe psychiatric conditions, Major Depressive disorder, Generalized Anxiety Disorder, Bipolar Disorder, Personality Disorder, OCD, Schizophrenia.
7. Severe neurological conditions, epilepsy, traumatic brain injury, and previous neurosurgery.
8. Habitual smokers and other habitual substance abuse or dependence on substances.

This pilot study will aim to recruit 60 women (18-36 years) to participate; 30 natural menstrual cycle/30 that use hormonal contraceptives.

The data collected during this study is not publicly available due to General Data Protection Regulations (GDPR) reasons.