Menstrual cycle length variation by demographic characteristics from the Apple Women's Health Study

Measurement of changes to the menstrual cycle: A transdisciplinary systematic review evaluating measure quality and utility for clinical trials

Despite the importance of menstruation and the menstrual cycle to health, human rights, and sociocultural and economic wellbeing, the study of menstrual health suffers from a lack of funding, and research remains fractured across many disciplines. We sought to systematically review validated approaches to measure four aspects of changes to the menstrual cycle-bleeding, blood, pain, and perceptions-caused by any source and used within any field. We then evaluated the measure quality and utility for clinical trials of the identified instruments. We searched MEDLINE, Embase, and four instrument databases and included peer-reviewed articles published between 2006 and 2023 that reported on the development or validation of instruments assessing menstrual changes using quantitative or mixed-methods methodology. From a total of 8,490 articles, 8,316 were excluded, yielding 174 articles reporting on 94 instruments. Almost half of articles were from the United States or United Kingdom and over half of instruments were only in English, Spanish, French, or Portuguese. Most instruments measured bleeding parameters, uterine pain, or perceptions, but few assessed characteristics of blood. Nearly 60% of instruments were developed for populations with menstrual or gynecologic disorders or symptoms. Most instruments had fair or good measure quality or clinical trial utility; however, most instruments lacked evidence on responsiveness, question sensitivity and/or transferability, and only three instruments had good scores of both quality and utility. Although we took a novel, transdisciplinary approach, our systematic review found important gaps in the literature and instrument landscape, pointing towards a need to examine the menstrual cycle in a more comprehensive, inclusive, and standardized way. Our findings can inform the development of new or modified instruments, which-if used across the many fields that study menstrual health and within clinical trials-can contribute to a more systemic and holistic understanding of menstruation and the menstrual cycle.

Chronicling menstrual cycle patterns across the reproductive lifespan with real-world data

The intricate hormonal and physiological changes of the menstrual cycle can influence health on a daily basis. Although prior studies have helped improve our understanding of the menstrual cycle, they often lack diversity in the populations included, sample size, and the span of reproductive and life stages. This paper aims to describe the dynamic differences in menstrual cycle characteristics and associated symptoms by age in a large global cohort of period-tracking application users. This work aims to contribute to our knowledge and understanding of female physiology at varying stages of reproductive aging. This cohort study included self-reported menstrual cycle and symptom information in a sample of Flo application users aged 18-55. Cycle and period length and their variability, and frequency of menstrual cycle symptom logs are described by the age of the user. Based on data logged by over 19 million global users of the Flo app, the length of the menstrual cycle and period show clear age-associated patterns. With higher age, cycles tend to get shorter (Cycle length: D ¯  = 1.85 days, Cohen's D = 0.59) and more variable (Cycle length SD: D ¯  = 0.42 days, Cohen's D = 0.09), until close to the chronological age (40-44) suggesting menopausal transition, when both cycles and periods become longer (Cycle length: D ¯  = 0.86 days, t = 48.85, Cohen's D = 0.26; Period length: D ¯  = 0.08, t = 15.6, Cohen's D = 0.07) and more variable (Cycle length SD: D ¯  = 2.80 days, t = 111.43, d = 0.51; Period length SD: D ¯  = 0.23 days, t = 67.81, Cohen's D = 0.31). The proportion of individuals with irregular cycles was highest in participants aged 51-55 (44.7%), and lowest in the 36-40 age group (28.3%). The spectrum of common menstrual cycle-related symptoms also varies with age. The frequency of logging of cramps and acne is lower in older participants, while logs of headache, backache, stress, and insomnia are higher in older users. Other symptoms show different patterns, such as breast tenderness and fatigue peaking between the ages of 20-40, or mood swings being most frequently logged in the youngest and oldest users. The menstrual cycle and related symptoms are not static throughout the lifespan. Understanding these age-related differences in cycle characteristics and symptoms is essential in understanding how best to care for and improve the daily experience for menstruators across the reproductive life span.

Menarche and Time to Cycle Regularity Among Individuals Born Between 1950 and 2005 in the US

Importance

Early menarche is associated with adverse health outcomes. Trends toward earlier menarche have been observed in the US, but data remain limited on differences by sociodemographic factors and body mass index (BMI). Time from menarche to cycle regularity is another understudied early-life characteristic with health implications.

Objectives

To evaluate the temporal trends and disparities in menarche and time to regularity and explore early-life BMI as a mediator.

Design, Setting, and Participants

This ongoing cohort study enrolled participants from an ongoing mobile application-based US cohort from November 14, 2019, to March 20, 2023.

Exposures

Birth year (categorized as 1950-1969, 1970-1979, 1980-1989, 1990-1999, and 2000-2005).

Main Outcomes and Measures

Main outcomes were age at menarche and time to regularity, which were self-recalled at enrollment. In addition, early (aged <11 years), very early (aged <9 years), and late (aged ≥16 years) age at menarche was assessed.

Results

Among the 71 341 female individuals who were analyzed (mean [SD] age at menarche, 12.2 [1.6] years; 2228 [3.1%] Asian, 3665 [5.1%] non-Hispanic Black, 4918 [6.9%] Hispanic, 49 518 [69.4%] non-Hispanic White, and 8461 [11.9%] other or multiple races or ethnicities), 5223 were born in 1950 to 1969, 12 226 in 1970 to 1979, 22 086 in 1980 to 1989, 23 894 in 1990 to 1999, and 7912 in 2000 to 2005. The mean (SD) age at menarche decreased from 12.5 (1.6) years in 1950 to 1969 to 11.9 (1.5) years in 2000 to 2005. The number of individuals experiencing early menarche increased from 449 (8.6%) to 1223 (15.5%), the number of individuals experiencing very early menarche increased from 31 (0.6%) to 110 (1.4%), and the number of individuals experiencing late menarche decreased from 286 (5.5%) to 137 (1.7%). For 61 932 participants with reported time to regularity, the number reaching regularity within 2 years decreased from 3463 (76.3%) to 4075 (56.0%), and the number not yet in regular cycles increased from 153 (3.4%) to 1375 (18.9%). The magnitude of the trend toward earlier menarche was greater among participants who self-identified as Asian, non-Hispanic Black, or other or multiple races (vs non-Hispanic White) (P = .003 for interaction) and among participants self-rated with low (vs high) socioeconomic status (P < .001 for interaction). Within a subset of 9865 participants with data on BMI at menarche, exploratory mediation analysis estimated that 46% (95% CI, 35%-61%) of the temporal trend in age at menarche was explained by BMI.

Conclusions and Relevance

In this cohort study of 71 341 individuals in the US, as birth year increased, mean age at menarche decreased and time to regularity increased. The trends were stronger among racial and ethnic minority groups and individuals of low self-rated socioeconomic status. These trends may contribute to the increase in adverse health outcomes and disparities in the US.

Irregular Cycles, Ovulatory Disorders, and Cardiometabolic Conditions in a US-Based Digital Cohort

Importance

Polycystic ovary syndrome (PCOS), characterized by irregular menstrual cycles and hyperandrogenism, is a common ovulatory disorder. Having an irregular cycle is a potential marker for cardiometabolic conditions, but data are limited on whether the associations differ by PCOS status or potential interventions.

Objective

To evaluate the association of PCOS, time to regularity since menarche (adolescence), and irregular cycles (adulthood) with cardiometabolic conditions.

Design, Setting, and Participants

This cross-sectional study used a large, US-based digital cohort of users of the Apple Research application on their iPhone. Eligibility criteria were having ever menstruated, living in the US, being at age of consent of at least 18 years (or 19 years in Alabama and Nebraska or 21 years in Puerto Rico), and being able to communicate in English. Participants were enrolled between November 14, 2019, and December 13, 2022, and completed relevant surveys.

Exposures

Self-reported PCOS diagnosis, prolonged time to regularity (not spontaneously establishing regularity within 5 years of menarche), and irregular cycles.

Main Outcomes and Measures

The primary outcome was self-reported cardiometabolic conditions, including obesity, prediabetes, type 1 and 2 diabetes, high cholesterol, hypertension, metabolic syndrome, arrhythmia, congestive heart failure, coronary artery disease, heart attack, heart valve disease, stroke, transient ischemic attack (TIA), deep vein thrombosis, and pulmonary embolism measured using descriptive statistics and logistic regression to estimate prevalence odds ratios (PORs) and 95% CIs. Effect modification by lifestyle factors was also estimated.

Results

The study sample (N = 60 789) had a mean (SD) age of 34.5 (11.1) years, with 12.3% having PCOS and 26.3% having prolonged time to regularity. Among a subset of 25 399 participants who completed the hormonal symptoms survey, 25.6% reported irregular cycles. In covariate-adjusted logistic regression models, PCOS was associated with a higher prevalence of all metabolic and several cardiovascular conditions, eg, arrhythmia (POR, 1.37; 95% CI, 1.20-1.55), coronary artery disease (POR, 2.92; 95% CI, 1.95-4.29), heart attack (POR, 1.79; 95% CI, 1.23-2.54), and stroke (POR, 1.66; 95% CI, 1.21-2.24). Among participants without PCOS, prolonged time to regularity was associated with type 2 diabetes (POR, 1.24; 95% CI, 1.05-1.46), hypertension (POR, 1.09; 95% CI, 1.01-1.19), arrhythmia (POR, 1.20; 95% CI, 1.06-1.35), and TIA (POR, 1.33; 95% CI, 1.01-1.73), and having irregular cycles was associated with type 2 diabetes (POR, 1.36; 95% CI, 1.08-1.69), high cholesterol (POR, 1.17; 95% CI, 1.05-1.30), arrhythmia (POR, 1.21; 95% CI, 1.02-1.43), and TIA (POR, 1.56; 95% CI, 1.06-2.26). Some of these associations were modified by high vs low body mass index or low vs high physical activity.

Conclusions and Relevance

These findings suggest that PCOS and irregular cycles may be independent markers for cardiometabolic conditions. Early screening and intervention among individuals with irregular menstrual cycles may be beneficial.

COVID-19 and abnormal uterine bleeding: potential associations and mechanisms

The impact of COVID-19 on menstruation has received a high level of public and media interest. Despite this, uncertainty exists about the advice that women and people who menstruate should receive in relation to the expected impact of SARS-CoV-2 infection, long COVID or COVID-19 vaccination on menstruation. Furthermore, the mechanisms leading to these reported menstrual changes are poorly understood. This review evaluates the published literature on COVID-19 and its impact on menstrual bleeding, discussing the strengths and limitations of these studies. We present evidence consistent with SARS-CoV-2 infection and long COVID having an association with changes in menstrual bleeding parameters and that the impact of COVID vaccination on menstruation appears less significant. An overview of menstrual physiology and known causes of abnormal uterine bleeding (AUB) is provided before discussing potential mechanisms which may underpin the menstrual disturbance reported with COVID-19, highlighting areas for future scientific study. Finally, consideration is given to the effect that menstruation may have on COVID-19, including the impact of the ovarian sex hormones on acute COVID-19 severity and susceptibility and reported variation in long COVID symptoms across the menstrual cycle. Understanding the current evidence and addressing gaps in our knowledge in this area are essential to inform public health policy, direct the treatment of menstrual disturbance and facilitate development of new therapies, which may reduce the severity of COVID-19 and improve quality of life for those experiencing long COVID.

Menstrual characteristics and associations with sociodemographic factors and self-rated health in Spain: a cross-sectional study

BACKGROUND

Evidence on how menstrual characteristics may differ based on socioeconomic factors and self-rated health is significantly scarce. The main aim of this study was to investigate the associations between menstrual characteristics, sociodemographic factors and self-rated health among women and people who menstruate (PWM) aged 18-55 in Spain.

METHODS

This cross-sectional study includes data from an online survey collected in March-July 2021 across Spain. Descriptive statistical analyses and multivariate logistic regression models were performed.

RESULTS

The analyses included a total of 19,358 women and PWM. Mean age at menarche was 12.4 (SD = 1.5). While 20.3% of our participants experienced a menstrual abundance over 80 ml, 64.1% reported having menstrual blood clots; 6.4% menstruated for longer than 7 days. 17.0% had menstrual cycles that were shorter than 21 days or longer than 35 days. Reports of moderate (46.3%) and high (22.7%) intensity menstrual pain were common. 68.2% of our participants experienced premenstrual symptoms in all or most cycles. The odds for lighter menstrual flow, shorter bleeding days and menstrual cycles were higher as age increased, and amongst participants with less educational attainment. Caregivers presented higher odds for abundant menstrual flow and longer menstruations. Reporting financial constraints and a poorer self-rated health were risk factors for abundant menstrual flow, menstrual blood clots, shorter/longer menstruations and menstrual cycles, premenstrual symptoms, moderate and intense menstrual pain.

CONCLUSIONS

This study suggests that age, educational attainment, caregiving, experiencing financial hardship and a poorer self-rated health may shape or mediate menstrual characteristics. It thus highlights the need to investigate and address social inequities of health in menstrual research.

Prolongation of the Menstrual Cycle After Receipt of the Primary Series and Booster Doses of mRNA Coronavirus Disease 2019 (COVID-19) Vaccination

OBJECTIVE

To quantitatively evaluate the effect of a booster vaccination dose against coronavirus disease 2019 (COVID-19) on menstrual cycle in a large-scale retrospective cohort study using a menstrual cycle tracking smartphone application (app).

METHODS

Prospectively or retrospectively recorded data, including the start and finish dates of menstrual cycles, were collected with the app. Detailed data on vaccinations, side effects, and participants' characteristics were retrospectively collected from a questionnaire on the app. For each COVID-19 vaccination shot (first, second, and third), within-individual changes in menstrual cycle length up to the fourth postvaccination cycle were evaluated.

RESULTS

Among the 7,376 and 6,873 participants who had the first and second COVID-19 vaccine doses in different menstrual cycles, respectively, menstrual cycles immediately after the vaccination (first postvaccination cycles) were an average of 0.22 days (95% CI, 0.06-0.39) and 0.37 days (95% CI, 0.20-0.54) longer than the prevaccination cycle. In contrast, among the 1,672 participants who received the first and second doses in the same cycle, the first postvaccination cycle was an average of 4.21 days (95% CI, 3.69-4.72) longer. The second to fourth postvaccination cycles returned to the level of the prevaccination cycle. However, among the 4,768 participants who had the third COVID-19 vaccine dose, the menstrual cycle immediately after the vaccination was an average of 1.20 days (95% CI, 1.00-1.40) longer, with prolongation of cycles of 0.27 days (95% CI, 0.10-0.44) to 0.41 days (95% CI, 0.22-0.59) persisting from the second to the fourth postvaccination cycle.

CONCLUSION

The booster shot against COVID-19 may have a greater and longer-lasting effect on menstrual cycles than the primary-series shots. Although the effect size was small, evidence on the side effects of immunization on menstruation should be accumulated.

The effects of oral contraceptives on resting autonomic function and the autonomic response to physiological stressors: a systematic review

PURPOSE

This systematic review aimed to summarize how oral contraceptives (OC) affect resting autonomic function and the autonomic response to a variety of physiological stressors.

METHODS

A search strategy was created to retrieve citations investigating physiological responses comparing OC users to non-users (NOC) in response to autonomic reflex activation.

RESULTS

A total of 6148 citations were identified across databases from inception to June 2, 2022, and 3870 citations were screened at the abstract level after deduplication. Then, 133 texts were assessed at full-text level, and only 40 studies met eligibility requirements. Included citations were grouped by the aspect of autonomic function assessed, including autonomic reflex (i.e., baroreflex, chemoreflex, mechanoreflex, metaboreflex, and venoarterial reflex), or indicators (i.e., heart rate variability, pulse wave velocity, and sympathetic electrodermal activity), and physiological stressors that may alter autonomic function (i.e., auditory, exercise, mental or orthostatic stress, altitude, cold pressor test, sweat test, and vasodilatory infusions).

CONCLUSION

OC influence the physiological responses to chemoreflex, mechanoreflex, and metaboreflex activation. In terms of autonomic indices and physiological stressors, there are more inconsistencies within the OC literature, which may be due to estrogen dosage within the OC formulation (i.e., heart rate variability) or the intensity of the stressor (exercise intensity/duration or orthostatic stress). Further research is required to elucidate the effects of OC on these aspects of autonomic function because of the relatively small amount of available research. Furthermore, researchers should more clearly define or stratify OC use by duration, dose, and/or hormone cycling to further elucidate the effects of OC.