Menstrual Cycle Characteristics of U. S. Adolescents According to Gynecologic Age and Age at Menarche

STUDY OBJECTIVE

To characterize typical menstrual cycle characteristics in adolescents and determine how these differ with age at menarche or years since menarche (gynecologic age).

METHODS

We surveyed 13-18-year-old U.S. users of the Clue app (N=6,486) and linked their responses to app-recorded cycle data (N=38,916 cycles). We analyzed cycle characteristics including cycle length, cycle variability, period length, experience of heavy flow, and dysmenorrhea in relation to gynecologic age and menarcheal age using mixed effects models.

RESULTS

With increasing gynecologic age, we observed dose-dependent associations of lower odds of cycle irregularity (defined as cycles that were highly variable, short, or long) and higher odds of reporting ≥1 day of heavy flow. Individuals <1-year post-menarche had lower odds of heavy flow (Odds Ratio (OR) = 0.3; 95% confidence interval (CI): 0.1, 0.6), and increased odds of having a highly variable cycle (OR=2.6; 95% CI: 1.3, 5.2) or short cycles (OR=5.0; 95% CI: 2.3, 11.0) compared to those who were 6+ years post-menarche. We also found associations with early and late age at menarche. Compared to menarcheal age of 14+ years, menarcheal age ≤10 years was associated with shorter cycle length (β = -1.63 days; 95% CI: -2.51, -0.75), increased odds of dysmenorrhea (OR=3.2; 95% CI: 2.3, 4.6), and decreased odds of high cycle variability (OR=0.8; 95% CI: 0.6, 1.0).

CONCLUSION

Cycle characteristics in adolescence are associated with menarcheal age and gynecologic age. Notably, highly variable cycles are common, especially among those with younger gynecologic age or older menarcheal age.

Well-being in healthy Icelandic women varies with extreme seasonality in ambient light

Seasonal variation in photoperiod may affect psychosocial and physical well-being in healthy persons. We tested this hypothesis in healthy pre-menopausal women, without a history of mood disorders, living year-round in Reykjavik, Iceland (64.1°N). Participants reported daily self-assessments of well-being throughout a complete ovulatory menstrual cycle in summer and/or winter (70% participated in both seasons). Scores for mood, cognitive acuity, social support, physical health and a composite of these four indicators were each significantly higher in summer than in winter (linear mixed effects models: p < .001 for each model); tiredness did not differ by season. The effect of season was not significantly changed by inclusion of body mass index and/or age as covariates. Some prior studies have been hampered by sparse time sampling, inattention to covariates and/or relying on recalled data. This is to our knowledge the first investigation to test the study hypothesis with daily real-time data spanning complete ovulatory menstrual cycles in each of two seasons. This dense sampling has revealed modest seasonal variation in well-being in healthy women. Daylength (sunlight exposure) is likely a major, but not necessarily sole, factor in these seasonal differences in well-being; temperature is likely less important given Iceland's relatively moderate (for its high latitude) seasonal temperature swings.

Associations Among Menstrual Cycle Length, Coronavirus Disease 2019 (COVID-19), and Vaccination

OBJECTIVE

To assess whether coronavirus disease 2019 (COVID-19) is associated with menstrual cycle length changes and, if so, how that compares with those undergoing vaccination or no event (control).

METHODS

We conducted a retrospective cohort analysis in which we analyzed prospectively tracked cycle-length data from users of a period tracker application who also responded to a survey regarding COVID-19 symptoms and vaccination. We restricted our sample to users aged 16-45 years, with normal cycle lengths (24-38 days) and regular tracking behavior during the five cycles around COVID-19 symptoms or vaccination or a similar time period for those experiencing no event (control group). We calculated the within-user change in cycle length (days) from the three consecutive cycles preevent average (either vaccination, disease, or neither; cycles 1-3) to the event (cycle 4) and postevent (cycle 5) cycles. We used mixed-effects models to estimate the age- and country-adjusted difference in change in cycle length across the groups.

RESULTS

We included 6,514 users from 110 countries representing 32,570 cycles (COVID-19 symptoms: 1,450; COVID-19 vaccination: 4,643; control: 421). The COVID-19 cohort experienced a 1.45-day adjusted increase in cycle length during cycle 4 (COVID-19) compared with their three preevent cycles (95% CI 0.86-2.04). The vaccinated group experienced a 1.14-day adjusted increase in cycle length during cycle 4 (COVID-19 vaccine) compared with their preevent average (95% CI 0.60-1.69). The control group (neither vaccine nor disease) experienced a 0.68-day decrease (95% CI -1.18 to -0.19) in a similar time period. Post hoc tests showed no significant differences in the magnitude of changes between the COVID-19 and vaccination cohorts. In both cohorts, cycle length changes disappeared in the postevent cycle.

CONCLUSION

Experiencing COVID-19 is associated with a small change in cycle length similar to COVID-19 vaccination. These changes resolve quickly within the next cycle.

Assessment of App-Based Versus Conventional Survey Modalities for Reproductive Health Research in India, South Africa, and the United States: Comparative Cross-Sectional Study

BACKGROUND

There is a widely acknowledged global need for more research on reproductive health (including contraception, menstrual health, sexuality, and maternal morbidities) and its impact on overall well-being. However, several factors-notably, high costs, considerable effort, and the sensitivity of these topics-impede the collection of the necessary data, especially in less accessible and lower-income populations. The burgeoning ownership of smartphones and growing use of menstrual tracking apps (MTAs) may present an opportunity to conduct reproductive health research with fewer impediments than those associated with conventional survey methods.

OBJECTIVE

The main objective was to ascertain the feasibility, potential usefulness, and limitations of conducting reproductive health research using a mainstream MTA.

METHODS

In each of the 3 countries, we evaluated questionnaire responses from (1) current users of an MTA (Clue) and (2) participants surveyed using conventional survey modalities (in-person interviews, SMS text messaging, and web-based questionnaires). We compared these responses with published data collected from large nationally representative benchmark samples (the United States Census and the Demographic and Health Surveys for South Africa and India).

RESULTS

Given a sufficiently large user base, app-distributed surveys were able to quickly capture large samples on par with other methods and at low cost, with the additional advantage of being able to deploy remotely and simultaneously across countries. In each country, neither the app nor the conventional modality sample emerged as a consistently closer match to the distributions of the demographic attributes and the patterns of contraceptive use reported for the respective benchmark sample. Despite efforts to obtain representative samples, the conventional modality samples sometimes over- and other times underrepresented some subgroups (eg, underrepresentation of married persons in the United States and overrepresentation of rural residents in India). In all 3 countries, app users were younger, more educated, more likely to be urban residents, and more likely to use nonhormonal rather than hormonal contraceptive methods compared with the respective national benchmark. App users, compared with the conventional modality samples, consistently reported being more comfortable discussing their menstrual periods with other persons (eg, family, friends, and health care providers), suggesting that MTA users may be more likely to respond truthfully to questions on sensitive or taboo health topics. The app samples' consistency across countries regarding users' demographic profiles, contraceptive choices, and personal attitudes toward menstruation supports the validity of making cross-country comparisons of survey findings for a given app's users.

CONCLUSIONS

MTAs such as Clue can provide a quick, scalable, and cost-effective method for collecting health data, including on sensitive topics, across a wide variety of settings and countries. With expanding global access to technology and the increasing use of these tools, consumer MTAs can be a viable survey modality to strengthen reproductive health research.

The Link Between Age and Partner Preferences in a Large, International Sample of Single Women

Women's capacity to reproduce varies over the life span, and developmental goals such as family formation are age-graded and shaped by social norms about the appropriate age for completing specific developmental tasks. Thus, a woman's age may be linked to her ideas about what an ideal partner should be like. With the goals of replicating and extending prior research, in this study we examined the role of age in women's partner preferences across the globe. We investigated associations of age with ideal long-term partner preferences in a cross-cultural sample of 17,254 single (i.e., unpartnered) heterosexual women, ages 18 to 67, from 147 countries. Data were collected via an online questionnaire, the Ideal Partner Survey. Confirming our preregistered hypotheses, we found no or only negligible age effects on preferences for kindness-supportiveness, attractiveness, financial security-successfulness, or education-intelligence. Age was, however, positively associated with preferences for confidence-assertiveness. Consistent with family formation goals, age was associated with an ideal partner's parenting intentions (high until approximately age 30, then decreasing afterward). Age range deemed acceptable (and in particular, the discrepancy between one's own age and the minimum ideal age of a partner) increased with age. This latter pattern also replicated in exploratory analyses based on subsamples of lesbian and bisexual women. In summary, age has a limited impact on partner preferences. Of the attributes investigated, only preference for confidence-assertiveness was linked with age. However, age range deemed acceptable and an ideal partner's parenting intention, a dimension mostly neglected in earlier research, substantially vary with age.

More than blood: app-tracking reveals variability in heavy menstrual bleeding construct

BACKGROUND

Heavy menstrual bleeding (HMB) is associated with impaired quality of life and may signal serious health problems. Unresolved challenges in measuring menstrual bleeding and identifying HMB have hampered research and clinical care. Self-reported bleeding histories are commonly used but these may be influenced by recall bias, personal beliefs regarding "normal" flow volume, and the experience of other physical symptoms or disruptions to daily life. The potential usefulness of menstrual-tracking mobile applications, which allow real-time user-entered data recording, for assessing HMB has not been studied. We evaluated recall bias in reported period duration, the relationship of tracked period duration and daily flow volume to subsequently reported period heaviness, variation in quality of life associated with increasing period heaviness, and the advantages and limitations of using app-tracked data for clinical and research purposes.

METHODS

An online questionnaire was distributed to current users of Clue, a commercially available menstrual health tracking app, asking them to characterize their last period. We compared responses to the user's corresponding Clue app-tracked data. The study sample comprised 6546 U.S.-based users (aged 18-45 years).

RESULTS

Increasing reported heaviness was associated with increasing app-tracked period length and days of heavy flow, impaired quality-of-life (especially body pain severity), and disrupted activities. Of those reporting having had a heavy/very heavy period, ~ 18% had not tracked any heavy flow, but their period length and quality-of-life indicators were similar to those who had tracked heavy flow. Sexual/romantic activities were the most affected across all flow volumes. Compared to app-tracked data, 44% recalled their exact period length; 83% recalled within ± 1 day. Overestimation was more common than underestimation. However, those with longer app-tracked periods were more likely to underestimate period length by ≥ 2 days, a pattern which could contribute to under-diagnosis of HMB.

CONCLUSION

Period heaviness is a complex construct that encapsulates flow volume and, for many, several other bleeding-associated experiences (period length, bodily impairments, disruptions of daily activities). Even very precise flow volume assessments cannot capture the multi-faceted nature of HMB as experienced by the individual. Real-time app-tracking facilitates quick daily recording of several aspects of bleeding-associated experiences. This more reliable and detailed characterization of bleeding patterns and experiences can potentially increase understanding of menstrual bleeding variability and, if needed, help to guide treatment.

Socioeconomic impacts on Andean adolescents’ growth

Background/Objectives

We evaluated potential socioeconomic contributors to variation in Andean adolescents’ growth between households within a peri-urban community undergoing rapid demographic and economic change, between different community types (rural, peri-urban, urban) and over time. Because growth monitoring is widely used for assessing community needs and progress, we compared the prevalences of stunting, underweight, and overweight estimated by three different growth references.

Methods

Anthropometrics of 101 El Alto, Bolivia, adolescents (Alteños), 11.0–14.9 years old in 2003, were compared between households (economic status assessed by parental occupations); to one urban and two rural samples collected in 1983/1998/1977, respectively; and to the WHO growth reference, a representative sample of Bolivian children (MESA), and a region-wide sample of high-altitude Peruvian children (Puno).

Results

Female Alteños’ growth was positively associated with household and maternal income indices. Alteños’ height averaged ∼0.8SD/∼0.6SD/∼2SDs greater than adolescents’ height in urban and rural communities measured in 1983/1998/1977, respectively. Overweight prevalence was comparable to the WHO, and lower than MESA and Puno, references. Stunting was 8.5/2.5/0.5 times WHO/MESA/Puno samples, respectively.

Conclusions/Implications

Both peri-urban conditions and temporal trends contributed to gains in Alteños’ growth. Rural out-migration can alleviate migrants’ poverty, partly because of more diverse economic options in urbanized communities, especially for women. Nonetheless, Alteños averaged below WHO and MESA height and weight medians. Evolved biological adaptations to environmental challenges, and the consequent variability in growth trajectories, favor using multiple growth references. Growth monitoring should be informed by community- and household-level studies to detect and understand local factors causing or alleviating health disparities.

A predictive model for next cycle start date that accounts for adherence in menstrual self-tracking

OBJECTIVE

The study sought to build predictive models of next menstrual cycle start date based on mobile health self-tracked cycle data. Because app users may skip tracking, disentangling physiological patterns of menstruation from tracking behaviors is necessary for the development of predictive models.

MATERIALS AND METHODS

We use data from a popular menstrual tracker (186 000 menstruators with over 2 million tracked cycles) to learn a predictive model, which (1) accounts explicitly for self-tracking adherence; (2) updates predictions as a given cycle evolves, allowing for interpretable insight into how these predictions change over time; and (3) enables modeling of an individual's cycle length history while incorporating population-level information.

RESULTS

Compared with 5 baselines (mean, median, convolutional neural network, recurrent neural network, and long short-term memory network), the model yields better predictions and consistently outperforms them as the cycle evolves. The model also provides predictions of skipped tracking probabilities.

DISCUSSION

Mobile health apps such as menstrual trackers provide a rich source of self-tracked observations, but these data have questionable reliability, as they hinge on user adherence to the app. By taking a machine learning approach to modeling self-tracked cycle lengths, we can separate true cycle behavior from user adherence, allowing for more informed predictions and insights into the underlying observed data structure.

CONCLUSIONS

Disentangling physiological patterns of menstruation from adherence allows for accurate and informative predictions of menstrual cycle start date and is necessary for mobile tracking apps. The proposed predictive model can support app users in being more aware of their self-tracking behavior and in better understanding their cycle dynamics.

Recognizing normal reproductive biology: A comparative analysis of variability in menstrual cycle biomarkers in German and Bolivian women

The idealized "normal" menstrual cycle typically comprises a coordinated ebb and flow of hormones over a 28-day span with ovulation invariably shown at the midpoint. It's a pretty picture-but rare. Systematic studies have debunked the myth that cycles occur regularly about every 28 days. However, assumptions persist regarding the extent and normalcy of variation in other cycle biomarkers. The processes of judging which phenotypic variants are "normal" is context dependent. In everyday life, normal is that which is most commonly seen. In biomedicine normal is often defined as an arbitrarily bounded portion of the phenotype's distribution about its statistical mean. Standards thus defined in one population are problematic when applied to other populations; population specific standards may also be suspect. Rather, recognizing normal female reproductive biology in diverse human populations requires specific knowledge of proximate mechanisms and functional context. Such efforts should be grounded in an empirical assessment of phenotypic variability. We tested hypotheses regarding cycle biomarker variability in women from a wealthy industrialized population (Germany) and a resource-limited rural agropastoral population (Bolivia). Ovulatory cycles in both samples displayed marked but nonetheless comparable variability in all cycle biomarkers and similar means/medians for cycle and phase lengths. Notably, cycle and phase lengths are poor predictors of mid-luteal progesterone concentrations. These patterns suggest that global and local statistical criteria for "normal" cycles would be difficult to define. A more productive approach involves elucidating the causes of natural variation in ovarian cycling and its consequences for reproductive success and women's health.

Mind the gap: Contesting normal/abnormal constructs of human biology and behaviors

Training in anthropology and evolutionary science ideally prepares scholars to recognize and challenge culturally grounded views of human variation. But upon inspection we find that idealized, and thus perhaps biased, conceptualizations of what is "normal" continue to permeate evaluations of human biology and behaviors. Each of the 13 contributions in this special issue on biological normalcy tackles these concerns as they pertain to some universal, but also variable, human biological or behavioral phenotype. These papers consider the ways in which the term "normal" is used in everyday life, in biomedicine, and in scientific studies to characterize some portion of the variability in a human phenotype. The contributors to this special issue, some of whom present original research findings, discuss the ongoing debates and challenges in the study of human biology and behavior, and critically examine how "normal" is used in their specific research area, thereby exposing and countering biases in the discourse on human phenotypic variation.

A Generative Modeling Approach to Calibrated Predictions: A Use Case on Menstrual Cycle Length Prediction

We explore how to quantify uncertainty when designing predictive models for healthcare to provide well-calibrated results. Uncertainty quantification and calibration are critical in medicine, as one must not only accommodate the variability of the underlying physiology, but adjust to the uncertain data collection and reporting process. This occurs not only on the context of electronic health records (i.e., the clinical documentation process), but on mobile health as well (i.e., user specific self-tracking patterns must be accounted for). In this work, we show that accurate uncertainty estimation is directly relevant to an important health application: the prediction of menstrual cycle length, based on self-tracked information. We take advantage of a flexible generative model that accommodates under-dispersed distributions via two degrees of freedom to fit the mean and variance of the observed cycle lengths. From a machine learning perspective, our work showcases how flexible generative models can not only provide state-of-the art predictive accuracy, but enable well-calibrated predictions. From a healthcare perspective, we demonstrate that with flexible generative models, not only can we accommodate the idiosyncrasies of mobile health data, but we can also adjust the predictive uncertainty to per-user cycle length patterns. We evaluate the proposed model in real-world cycle length data collected by one of the most popular menstrual trackers worldwide, and demonstrate how the proposed generative model provides accurate and well-calibrated cycle length predictions. Providing meaningful, less uncertain cycle length predictions is beneficial for menstrual health researchers, mobile health users and developers, as it may help design more usable mobile health solutions.

Field methods and strategies for assessing female reproductive functioning

A detailed understanding of female reproductive functioning is important to many disciplines including anthropology, evolutionary theory, demography, psychology, and biomedicine. In this article, I describe strategies and methods that have been used successfully in community-based studies of human reproduction, many in remote locales, to produce high quality biomarker data. These techniques are applicable to a wide range of research questions and populations, and to persons from adolescence through senescence. I give particular attention to the inherent challenges imposed by the cyclical and somewhat unpredictable nature of the hypothalamic-pituitary-ovarian axis including the necessity and difficulty of ascertaining the timing and occurrence of ovulation, the limits of different sampling regimes for capturing fluctuations in reproductive hormones, and the critical importance of recognizing and, when possible, reducing selection bias. I discuss the relative advantages and disadvantages of collecting saliva, urine, and dried blood spots, and describe some of the subtleties involved in collecting contamination-free samples. Once samples are collected, they must be stored in a manner that minimizes degradation; I describe techniques to keep samples cold even without access to electricity or dry ice. I also discuss various issues that should be considered during initial discussions with a laboratory and when samples are assayed by the laboratory. I include examples of techniques that have worked well in actual field studies, and examples of flawed analytical approaches that should be avoided. With these and other tools, even under technology-sparse conditions, researchers can investigate variability in human physiology across the breadth of human habitats.

Mobile sex-tech apps: How use differs across global areas of high and low gender equality

Digital technologies are increasingly intertwined into people's sexual lives, with growing scholarly interest in the intersection of sex and technology (sex-tech). However, much of the literature is limited by its over emphasis on negative outcomes and the predominance of work by and about North Americans, creating the impression that sex-tech is largely a Western phenomenon. Based on responses from 130,885 women in 191 countries, we assessed how women around the world interact with mobile technology for sex-related purposes, and whether in areas of greater gender inequality, technological accessibility may be empowering women with knowledge about sexuality. We investigated women's use of technology to find sexual partners, learn about sex and improve their sexual relationships, and track their own sexual health. About one-fifth reported using mobile apps to find sexual partners. This use varied by region: about one-third in Oceania, one-fourth in Europe and the Americas, and one-fifth in Asia and Africa. Staying connected when apart was the most commonly selected reason for app use with a sexual partner. About one-third had used an app to track their own sexual activity. Very few reported that the app they used to improve their sexual relationships was detrimental (0.2%) or not useful (0.6%). Women in countries with greater gender inequality were less likely to have used mobile apps to find a sexual partner, but nearly four times more likely to have engaged in sending and receiving sexts. To our knowledge, this study provides the most comprehensive global data on sex-tech use thus far, demonstrates significant regional variations in sex-tech use, and is the first to examine women's engagement in sex-related mobile technology in locations with greater gender disparities. These findings may inform large-scale targeted studies, interventions, and sex education to improve the lives of women around the world.

Characterizing physiological and symptomatic variation in menstrual cycles using self-tracked mobile-health data

The menstrual cycle is a key indicator of overall health for women of reproductive age. Previously, menstruation was primarily studied through survey results; however, as menstrual tracking mobile apps become more widely adopted, they provide an increasingly large, content-rich source of menstrual health experiences and behaviors over time. By exploring a database of user-tracked observations from the Clue app by BioWink GmbH of over 378,000 users and 4.9 million natural cycles, we show that self-reported menstrual tracker data can reveal statistically significant relationships between per-person cycle length variability and self-reported qualitative symptoms. A concern for self-tracked data is that they reflect not only physiological behaviors, but also the engagement dynamics of app users. To mitigate such potential artifacts, we develop a procedure to exclude cycles lacking user engagement, thereby allowing us to better distinguish true menstrual patterns from tracking anomalies. We uncover that women located at different ends of the menstrual variability spectrum, based on the consistency of their cycle length statistics, exhibit statistically significant differences in their cycle characteristics and symptom tracking patterns. We also find that cycle and period length statistics are stationary over the app usage timeline across the variability spectrum. The symptoms that we identify as showing statistically significant association with timing data can be useful to clinicians and users for predicting cycle variability from symptoms, or as potential health indicators for conditions like endometriosis. Our findings showcase the potential of longitudinal, high-resolution self-tracked data to improve understanding of menstruation and women's health as a whole.

Decision making over condom use during menses to avert sexually transmissible infections

Background The aim of this study was to test the hypothesis that receptive partners in penile-vaginal intercourse (PVI) who exercise independent decision making over condom use during menses do so to avert sexually transmissible infection (STI) transmission or acquisition.

METHODS

Data were collected through a partnership with Clue, the industry-leading female health app. A brief web-based questionnaire was developed, translated into 10 languages, and made accessible via a URL link sent to Clue users and posted on social media. Inclusion criteria were: age ≥14 years, not being currently pregnant and engaging in PVI and condom use during menses in the past 3 months. The analytical subsample comprised 12889 respondents residing in 146 countries.

RESULTS

Twenty per cent indicated independent decision making about condom use during menses. Independent decision making was associated with lower odds of reporting that condoms were used for contraception (adjusted odds ratio (aOR) 0.65; 99% confidence interval (CI) 0.57-0.73) and higher odds that they were used for the prevention of STIs (aOR 1.44; 99% CI 1.28-1.61). A third significant finding pertained to always using condoms during menses; this was less likely among those indicating independent (female only) decision making (aOR 0.69; 99% CI 0.62-0.78). Non-significant associations with another two outcomes were found: protecting the partner against menstrual blood and protecting themselves against semen.

CONCLUSIONS

Findings from people in 146 countries strongly support the hypothesis that those exercising independent decision making over condom use during menses do so to avert STI transmission or acquisition. That only one-fifth of this global sample reported this type of independent decision making suggests that empowerment-oriented (structural-level) interventions may be advantageous for individuals who are the receptive partner in PVI that occurs during menses.

Community, household, and individual correlates of sleep behaviors in Guyanese female youth

OBJECTIVES

Chronic sleep loss among youth is a worldwide health problem. Since research on its predictors is often limited to high-income countries, it is unclear if these findings are generalizable to all populations. To address this gap from an ecological perspective, we evaluated the associations between adolescents' sleep behaviors and several factors at the community, household, and individual levels in a middle-income country.

METHODS

This was a cross-sectional study of 73 girls (mean age = 14.5 y; range = 11-18 y) in rural and urban communities in Guyana. Sleep behaviors (nap-duration, bedtime, rise-time, night-bed-duration, and sleep-duration) were assessed with interviews and monitored up to 7 consecutive days using waist-worn accelerometers.

RESULTS

Similar to other settings, Guyanese urban youth reported significantly later bedtimes than rural youth, and increasing age was associated with later bedtime and shorter night-bed-duration. In contrast to the association observed in high-income countries, increasing household poverty scores in Guyana were associated with longer night-bed-duration.

CONCLUSIONS

Although the relationships between locale, age, and sleep in Guyana paralleled patterns seen in high-income countries, the positive relationship between poverty and sleep diverges from previous reports. These findings suggest that predictors of chronic sleep loss seen in high-income countries are likely to differ from those in middle- and low-income countries. More sleep studies in underrepresented populations are needed to gain a comprehensive understanding of adolescent sleep behavior and its correlates.

Vaginal Glycogen, Not Estradiol, Is Associated With Vaginal Bacterial Community Composition in Black Adolescent Women

PURPOSE

The purpose of this study was to characterize the composition of vaginal bacterial communities in a cohort of black adolescent women and to determine how the species composition of these communities correlates with levels of estradiol, glycogen, and stress.

METHODS

Twenty-one black adolescent women were sampled longitudinally. The composition of their vaginal communities was determined by analyzing the sequences of the V1-V3 regions of 16S rRNA genes, and they were grouped based on patterns in species abundances. The relationships between estradiol, glycogen, psychosocial stress, and the composition of these communities were assessed.

RESULTS

Vaginal communities could be distinguished and classified into three groups that differed in the abundances of Lactobacillus. Eighty-one percent of study participants had communities dominated by species of Lactobacillus. Glycogen levels were higher in communities dominated by one or multiple species of Lactobacillus compared with those having low proportions of Lactobacillus. Estradiol and psychosocial stress measurements did not differ among the three groups, whereas estradiol and glycogen exhibited a weak positive relationship that was not statistically significant.

CONCLUSIONS

The findings of this pilot study suggest that glycogen levels are associated with vaginal community composition in young black women; however, estradiol and psychosocial stress are not. In addition, the results suggest there is no simple relationship between levels of estradiol and the production of vaginal glycogen.

Corrigendum to: Decision making over condom use during menses to avert sexually transmissible infections

Background:The aim of this study was to test the hypothesis that receptive partners in penile-vaginal intercourse (PVI) who exercise independent decision making over condom use during menses do so to avert sexually transmissible infection (STI) transmission or acquisition. Methods: Data were collected through a partnership with Clue, the industry-leading female health app. A brief web-based questionnaire was developed, translated into 10 languages, and made accessible via a URL link sent to Clue users and posted on social media. Inclusion criteria were: age ≥14 years, not being currently pregnant and engaging in PVI and condom use during menses in the past 3 months. The analytical subsample comprised 12889 respondents residing in 146 countries. Results: Twenty per cent indicated independent decision making about condom use during menses. Independent decision making was associated with lower odds of reporting that condoms were used for contraception (adjusted odds ratio (aOR) 0.65; 99% confidence interval (CI) 0.57-0.73) and higher odds that they were used for the prevention of STIs (aOR 1.44; 99% CI 1.28-1.61). A third significant finding pertained to always using condoms during menses; this was less likely among those indicating independent (female only) decision making (aOR 0.69; 99% CI 0.62-0.78). Non-significant associations with another two outcomes were found: protecting the partner against menstrual blood and protecting themselves against semen. Conclusions: Findings from people in 146 countries strongly support the hypothesis that those exercising independent decision making over condom use during menses do so to avert STI transmission or acquisition. That only one-fifth of this global sample reported this type of independent decision making suggests that empowerment-oriented (structural-level) interventions may be advantageous for individuals who are the receptive partner in PVI that occurs during menses.

Impacts of nocturnal breastfeeding, photoperiod, and access to electricity on maternal sleep behaviors in a non-industrial rural Bolivian population

OBJECTIVES

We tested 4 main predictions, derived from life history theory and self-evident human diurnality, regarding maternal sleep behaviors in a non-industrialized population in which mother-nursling co-sleeping is universal and prolonged: (1) Night breastfeeding incurs a sleep cost to co-sleeping mothers; (2) Night breastfeeding increases with infant age, causing mothers to sleep less; (3) Sleep duration co-varies with darkness duration; (4) Access to electricity reduces sleep duration.

DESIGN

Mothers self-recorded and reported nursing and sleep behaviors for a 48-hour period once per month (median = 5 months).

SETTING

Rural Bolivian altiplano homesteads, primarily reliant on agropastoralism, scattered throughout the countryside surrounding a main town (altitude 3800 m; 17°14'S, 65°55'W; darkness duration 10-12 hours over the year).

PARTICIPANTS

One hundred eighty-four co-sleeping mother-infant pairs (infant age 22-730 days).

MEASUREMENTS

Breastfeeding frequency, and retiring and rising times for 885 48-hour observation periods.

RESULTS

Maternal sleep duration covaried with darkness duration. Sleep duration was shorter in those with access to electricity (ie, living nearer to town) than those without access (more distant homesteads). Night breastfeeding rate was fairly steady until it began to decline after the first year postpartum. At a given infant age, higher night breastfeeding rates were associated with less maternal sleep. As their infants aged, mothers without electricity slept more, whereas mothers with access slept less.

CONCLUSIONS

During the first year postpartum, more frequent night nursing shortens maternal sleep more than any other predictor variable. For older infants, the effect of night nursing diminishes, and even modest "modernization" (eg, access to electricity) is associated with shorter maternal sleep.

Variance in Mood Symptoms Across Menstrual Cycles: Implications for Premenstrual Dysphoric Disorder

Premenstrual dysphoric disorder (PMDD) remains a controversial diagnosis: Some authors have argued that it pathologizes normal mood changes, and others have questioned the need for daily mood reports across multiple cycles. In the present study, we examined changes in mood among psychologically healthy young participants with regular menstrual cycles. We collected daily reports of negative mood (depression, nervousness, irritability, and fatigue) across two to six consecutive cycles from 27 participants aged 18-35 years, and we used variance decomposition analyses to examine how much of the variance in these daily reports was due to day, cycle, and individual. The majority of variance (79%-98%) was due to daily fluctuations and did not conform to a standard pattern of premenstrual rise/postmenstrual fall. These findings suggest that PMDD is not simply an exaggeration of mood patterns typical for psychologically healthy people. Individual patterns were relatively stable from cycle to cycle; thus tracking deviations from a patient's own normative mood patterns may have greater clinical utility than deviation from a presumptive norm.

Factors Influencing the Use of Biomedical Health Care by Rural Bolivian Anemic Women: Structural Barriers, Reproductive Status, Gender Roles, and Concepts of Anemia

METHODS

Non-pregnant women from a rural town and its surrounding region were tested for anemia. During phase 1 (n = 181), anemic women received a written recommendation for low-cost purchase of iron pills at the nearest health center. They were subsequently interviewed on their actions and experiences.

RESULTS

Estimated anemia prevalence among these non-pregnant women was 50% higher than the national average. Despite holding conceptualizations of anemia generally aligned with biomedical concepts, only 40% of anemic women attempted to obtain iron supplements from the health center. Town residents were about twice as likely to attempt to purchase pills as outside-town residents. Town women who were concurrently breastfeeding and menstruating, considered anemia most serious for women, and considered family health the shared responsibility of spouses were most likely to decide to purchase iron pills. Age, education, or native language did not negatively influence this health care behavior.

CONCLUSIONS

Securing iron supplements involves individual trade-offs in the allocation of time, cost and effort. Nonetheless, suitably tailored programs can potentially harness local perceptions in the service of reducing anemia. Because of their comparatively high motivation to obtain iron supplements, targeting concurrently breastfeeding and menstruating women could have a positive cascade effect such that these women continue attending to their iron needs once they stop breastfeeding and if they become pregnant again. Because a sense of shared responsibility for family health appears to encourage women to attend to their own health, programs for women could involve their spouses. Complementing centralized availability, biomedical and traditional healers could distribute iron supplements on rotating visits to outlying areas and/or at highly attended weekly markets.

Links among inflammation, sexual activity and ovulation: Evolutionary trade-offs and clinical implications

Inflammation in healthy sexually active women decreased at midcycle, around ovulation, which may have evolved to promote conception.

Background and objectives: We examined a mechanism that may coordinate trade-offs between reproduction and immune response in healthy women, namely, changes in inflammation across the ovarian cycle.

Methodology: We investigated C-reactive protein (CRP), an inflammation marker, across two consecutive ovarian cycles in 61 Bolivian women. Participants provided saliva samples every other day, and dried blood spots on 5–6 days spread across weeks 2–3 of each cycle. Cycles were characterized as ovulatory/anovulatory based on profiles of reproductive hormones. Participants also reported whether they were sexually partnered with a male or sexually abstinent during the study.

Results: High early-cycle, but not late-cycle, CRP was associated with anovulation. High inflammation at the end of one cycle was not associated with anovulation in the subsequent cycle. Among ovulatory cycles, women with sexual partners had significantly lower CRP at midcycle, and higher CRP at follicular and luteal phases; in contrast, sexually abstinent women had little cycle-related change in CRP. In anovulatory cycles, partnership had no effect on CRP. CRP varied significantly with socioeconomic status (higher in better-off than in poorer women).

Conclusions and implications: These findings suggest that the cycle-specific effect of inflammation on ovarian function may be a flexible, adaptive mechanism for managing trade-offs between reproduction and immunity. Sociosexual behavior may moderate changes in inflammation across the ovarian cycle, suggesting that these shifts represent evolved mechanisms to manage the trade-offs between reproduction and immunity. Clinically, these findings support considering both menstrual cycle phase and sexual activity in evaluations of pre-menopausal women’s CRP concentrations.

Fifty fertile years: anthropologists' studies of reproduction in high altitude natives

Early European colonists of the Andes had difficulties in reproducing, a fact that underpins the hypothesis that reproduction is impaired amongst all humans at high altitudes. Yet a 16th century missionary wrote, "… the Indians are healthiest and where they multiply the most prolifically is in these same cold air-tempers, … [yet most children of the Spaniards] when born in such regions do not survive." These observations suggest that humans at high altitudes are subjected to strong natural selection from hypoxia, cold and limited food sources and, furthermore, that human populations can and have adapted, and continue to adapt, to these conditions. Informed by multiple approaches and theoretical frameworks, anthropologists have investigated to what extent and precisely how high altitude environments impact human reproductive functioning and fertility. Analyses of the proximate determinants of natural fertility suggest that behaviors (breast/infant feeding practices in the Andes, and marriage practices and religious celibacy in the Himalaya) are major determinants of fertility in high altitude populations. Furthermore, data from Project REPA (Reproduction and Ecology in Provincía Aroma), a longitudinal study in rural Bolivia, demonstrate that fecundity is not impaired in this indigenous altiplano population, and that the risk for early pregnancy loss (EPL) is not elevated by environmental hypoxia but does vary seasonally with the agricultural cycle (contra to the assumption that EPLs are due almost entirely to genetically flawed concepti). This review discusses these and other findings that reveal the complex and dynamic adaptations of human reproductive functioning in high altitude environments.

Darwin's legacy: an evolutionary view of women's reproductive and sexual functioning

On the Origin of species, published just over 150 years ago, has deeply influenced thinking in both scientific and wider communities. Darwin's legacy includes recognition of the fact that all organisms evolve; that variation within and between species is natural and normal; and that an evolutionary approach to understanding the sources and consequences of this variation comprises theoretical frameworks, testable hypotheses, and rigorously collected evidence. With an eye toward facilitating communication and productive collaboration among researchers from different intellectual traditions who nonetheless share a common interest in women's reproductive and sexual functioning, we discuss evolutionary concepts and models, summarize the known variability in ovarian functioning and consider the implications of this variability for conducting sex research, and evaluate the relative merits of various biomarkers that serve as proxy measurements of a woman's reproductive and hormonal status. With these perspectives and methods from reproductive ecology at hand, we examine several contentious issues: the links between hormones and sexuality in premenopausal and perimenopausal women, the causes of premenstrual syndrome, and the existence (or not) of menstrual synchrony. In none of these cases is as much known as is often claimed. In each, there are abundant opportunities for innovative, albeit challenging, research.

Seasonal and circadian variation in salivary testosterone in rural Bolivian men

Testosterone (T) plays a key role in the increase and maintenance of muscle mass and bone density in adult men. Life history theory predicts that environmental stress may prompt a reallocation of such investments to those functions critical to survival. We tested this hypothesis in two studies of rural Bolivian adult men by comparing free T levels and circadian rhythms during late winter, which is especially severe, to those in less arduous seasons. For each pair of salivary T(AM)/T(PM) samples (collected in a approximately 12-h period), circadian rhythm was considered classic (C(CLASSIC)) if T(AM) > 110%T(PM), reverse (C(REVERSE)) if T(PM) > 110%T(AM), and flat (C(FLAT)) otherwise. We tested the hypotheses that mean T(AM) > mean T(PM) and that mean T(LW) < mean T(OTHER) (LW = late winter, OTHER = other seasons). In Study A, of 115 T(PM)-T(AM) pairs, 51% = C(CLASSIC), 39% = C(REVERSE), 10% = C(FLAT); in Study B, of 184 T(AM)-T(PM) pairs, 55% = C(CLASSIC), 33% = C(REVERSE), 12% = C(FLAT). Based on fitting linear mixed models, in both studies T(OTHER-AM) > T(OTHER-PM) (A: P = 0.035, B: P = 0.0005) and T(OTHER-AM) > T(LW-AM) (A: P = 0.054, B: P = 0.007); T(PM) did not vary seasonally, and T diurnality was not significant during late winter. T diurnality varied substantially between days within an individual, between individuals and between seasons, but neither T levels nor diurnality varied with age. These patterns may reflect the seasonally varying but unscheduled, life-long, strenuous physical labor that typifies many non-industrialized economies. These results also suggest that single morning samples may substantially underestimate peak circulating T for an individual and, most importantly, that exogenous signals may moderate diurnality and the trajectory of age-related change in the male gonadal axis.

Evolutionary Models of Women's Reproductive Functioning

Life history theory posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. Several physiological and behavioral mechanisms modulate reproductive effort in human females. This review focuses on the hormonal changes that vary the probability of ovulation, conception, and/or continuing pregnancy and discusses evolutionary models that predict how and why these hormonal changes occur. Anthropological field studies have yielded important insights into the environmental correlates of variation in ovarian steroids, but much remains to be learned about the evolutionary determinants, proximate mechanisms, and demographic significance of variation in women's reproductive functioning.

A prospective study of early pregnancy loss in humans

OBJECTIVE

To test two hypotheses: In spontaneous conceptions, early pregnancy loss (EPL) is associated with [1] inadequate luteal (ovarian) P, and/or [2] elevated follicular (adrenal) P.

DESIGN

A population-based prospective study.

SETTING

Thirty rural Bolivian communities.

PATIENT(S)

Women volunteers (n = 191), 19-40 years old, in stable sexual unions and not using contraception.

INTERVENTION(S)

Collection of serial saliva samples throughout sequential ovarian cycles and urine samples during late luteal phases. Collections continued throughout pregnancy for each detected conception.

MAIN OUTCOME MEASURE(S)

Occurrence of spontaneous conceptions and subsequent outcomes. Salivary concentrations of P. Test for elevated urinary human chorionic gonadotropin (hCG).

RESULT(S)

Luteal (through implantation) P levels were similar in pregnancies lost within 5 weeks after conception (EPL; n = 8) and those pregnancies that were maintained longer (sustained conceptions, SC; n = 32). Follicular P was significantly higher in EPL than in SC.

CONCLUSION(S)

[1] Elevated follicular P was associated with EPL in natural conceptions in healthy women. [2] Early pregnancy loss exhibits absolute luteal P levels comparable to SC, but lower luteal/follicular P ratios.

Hormonal Contraception and Physiology: A Research-based Theory of Discontinuation Due to Side Effects

Side effects influence the acceptability and continuation of hormonal contraceptives. Counseling the client about the management of side effects is a principal approach advocated for increasing continuation. Evidence of a biological basis for variation in women's tolerance of hormonal contraceptives argues, however, that greater attention should be given to altering the product rather than principally attempting to alter a woman's ability to deal with the product. Discontinuation rates for hormonal contraceptives, largely attributable to side effects and health concerns, are high in nearly all less-developed countries for which Demographic and Health Survey data are available. Oral contraceptives appear to be particularly problematic for Latin American women, most notably in Bolivia. Clinical trials suggest substantial variation in the physiological response to exogenous hormones, and new evidence confirms the hypothesis that the normal hormonal profiles of Bolivian women are significantly lower than those of women in the United States. These findings suggest a need for more population-specific physiological research linked to analyses of the possible association between endogenous hormone differences and contraceptive continuation. Appropriately adjusting the level of the steroid delivered may benefit women's health and improve the acceptability and continuation of hormonal contraceptives.

A number no greater than the sum of its parts: the use and abuse of heritability

Though widely used in quantitative genetics, in the study of human variation perhaps no statistic is more easily misinterpreted than heritability. While the contribution of genetic heritage to complex biological and behavioral phenotypes cannot be lightly dismissed, nonetheless we remain profoundly ignorant of how that legacy plays out in any environmental context. To be sure, it is not reducible to a single number. Nor does the preference among anthropologists for analyzing biological rather than behavioral phenotypes improve what heritability can reasonably say about the sources of human variation. This paper discusses the meaning of heritability, the methods for its estimation, the fallacies underlying its misuse, and its utility for inquiries in evolutionary anthropology and epidemiology. Progress in anthropological genetics will be realized through greater sophistication in study designs, including the measurement of environmental (physical and sociocultural) variation and the judicious choice of phenotypes for study. Elucidating the ontogenetic processes underlying adaptive plasticity is particularly critical to understanding the evolution of human biological variation. Such advancements will also shed light on the feasibility of genotype-targeted biomedical treatments. Failure to appreciate the limits of such approaches can divert resources from demonstrably effective environmentally based health interventions that benefit entire populations. Simplistic notions of genetic determinism should be challenged for the sake of our theories and the well-being of larger communities. As exemplified by the work of Frank B. Livingstone, anthropological genetics is at its best when incorporating anthropology into the study of human phenotypic variation.

Interpopulational differences in progesterone levels during conception and implantation in humans

Clinical studies of women from the United States demonstrate a sensitivity of the ovarian system to energetic stress. Even moderate exercise or caloric restriction can lead to lower progesterone levels and failure to ovulate. Yet women in many nonindustrial populations experience as many as a dozen pregnancies in a lifetime despite poor nutritional resources, heavy workloads, and typical progesterone levels only about two-thirds of those of U.S. women. Previous cross-sectional studies of progesterone may, however, suffer from inadvertent selection bias. In a noncontracepting population, the most fecund women, who might be expected to have the highest progesterone, are more likely to be pregnant or breastfeeding and hence unavailable for a cross-sectional study of the ovarian cycle. The present longitudinal study was designed to ascertain whether lower progesterone also characterizes conception, implantation, and gestation in women from nonindustrialized populations. We compared rural Bolivian Aymara women (n = 191) to women from Chicago (n = 29) and found that mean-peak-luteal progesterone in the ovulatory cycles of Bolivian women averaged approximately 71% that of the women from Chicago. In conception cycles, progesterone levels in Bolivian women during the periovulatory period were approximately 63%, and during the peri-implantation period were approximately 50%, those of the U.S. women. These observations argue that lower progesterone levels typically characterize the reproductive process in Bolivian women and perhaps others from nonindustrialized populations. We discuss the possible proximate and evolutionary explanations for this variation and note the implications for developing suitable hormonal contraceptives and elucidating the etiology of cancers of the breast and reproductive tract.

The proximate determinants of fertility in populations exposed to chronic hypoxia

It has been hypothesized that hypoxia reduces fertility, but comparative studies of high and low altitude populations have been unable to verify or refute this proposal because it is difficult to control for the behavioral and sociocultural factors that may also either underlie fertility differentials or compensate for physiological changes caused by varying partial pressure of oxygen. Taken collectively, estimates of fertility in populations exposed to chronic hypoxia range widely and do not suggest any reproductive patterns specific to high altitude. Here we review the available data from the Andes and the Himalaya on the proximate determinants of fertility, that set of factors through which any and all environmental, behavioral, and sociocultural factors must act to influence fertility levels. Although hypoxia could potentially affect some of these factors, there is no unequivocal evidence that this occurs in human populations indigenous to high altitude. At this time, it appears that local variations in infant feeding beliefs and practices, often coupled with prolonged breast-feeding, play a major role in determining fertility variation in Andean populations. In the Himalaya, large numbers of adults are not in sanctioned sexual unions as a consequence of polyandrous marriage practices and religious celibacy. The absence of a clear negative effect of hypoxia on fertility in populations indigenous to high altitude, even though migrants report reproductive difficulties, argues that these populations have adapted to the conditions at high altitude. The experimental and clinical evidence presented in this issue suggests proximate mechanisms by which such adaptation, shaped by natural selection and developmental processes, is possible.

Epidemiological transitions, reproductive health, and the Flexible Response Model

In concert with improving standards of living since the mid-19th century, chronic and non-infectious diseases replaced infectious diseases as the major causes of mortality in more developed countries. Thus, economic development has been seen as one strategy to improve women's reproductive health. However, rates of two of the major contributors to women's illness, maternal mortality and breast cancer, do not correspond well with the level of economic development. Drawing upon our longitudinal study of reproductive functioning among rural Bolivians (Project Reproduction and Ecology in Provincia Aroma (REPA)), we propose an evolutionary model to explain variation in certain aspects of women's reproductive health. Our findings suggest new avenues of inquiry into the determinants of reproductive health and have implications for improving the well-being of women worldwide.

Salivary progesterone levels and rate of ovulation are significantly lower in poorer than in better-off urban-dwelling Bolivian women

BACKGROUND

Agriculturalists in less-developed countries (LDC) have lower progesterone levels than urban industrialized populations. However, it is unknown if urban LDC populations are also relatively lower. We tested whether urban Bolivia samples-poorer (Bol-p) and better-off (Bol-b)-have lower progesterone than a Chicago (USA) sample, and whether progesterone and rate of ovulation are lower in Bol-p than in Bol-b.

METHODS

Serial salivary samples collected from Bolivians, screened according to strict exclusion criteria during two complete menstrual cycles, were radioimmunoassayed for progesterone; anthropometrics were collected at mid-follicular and mid-luteal phases.

RESULTS

Progesterone levels are lower in the Bolivia samples, and higher in the Bol-b than Bol-p; ovulation rate is greater in Bol-b than Bol-p. For only ovulatory cycles, mean-follicular-P (pmol/l), mean-luteal-P (pmol/l), and mean-peak-P (pmol/l) are respectively 65, 142 and 208 in Bol-p; 76, 167 and 232 in Bol-b; and 96, 240 and 330 in Chicago. Principal components representing body-size and progesterone level are positively correlated (r = 0.404, P = 0.005).

CONCLUSIONS

Progesterone levels appear to be influenced by chronic and acute ecological conditions, evidenced by the association with body-size and the probability of ovulation respectively. These findings have implications for understanding cancer aetiology, developing population-appropriate hormonal contraceptives, and modelling the evolution and functioning of the reproductive system.

Household economic strategies and nutritional anthropometry of women in American Samoa and highland Bolivia

This study compares findings from research projects involving different genetic, environmental, and cultural contexts: a study of lifestyle and health from American Samoa (ASLS) and the Bolivian project. Reproduction and Ecology in Provincia Aroma (REPA). This paper presents analyses of varying economic strategies and their association with nutritional status indicators in each population. The ASLS sample includes 66 Samoan women and the REPA sample includes 210 Aymara women. Principle components analysis of household economic resources within each sample extracted two significant factors: one represents modernizing influences including education and occupational status, and the other represents ethnographically salient traditional economic behavior. The traditional pattern includes adding household members in Samoa and selling agricultural products in Bolivia. This analysis places each woman along two continua, traditional and modern, based on her household mobilization of economic resources, permitting an understanding of the patterns underlying household economic behavior that is not possible in univariate analyses of socioeconomic variables. For the Bolivian women the strategy involving more education and higher occupational status was associated with higher measures of several nutritional status indicators, including body mass index, arm muscle area, and peripheral skinfolds. But among the Samoan women, where substantial obesity was the norm, there were no significant differences in anthropometric measurements based on economic strategies. These data argue for the importance of directly measuring the potential consequences of variation in household economic strategies rather than merely inferring such, and of assessing ethnographically relevant aspects of household economic production rather than limiting analyses to non-context-specific economic indicators such as income. This focus on household strategy is likely to be fruitful especially where economic and nutritional conditions are marginal. The findings from Bolivia also support efforts in developing countries to improve girls' education, and thereby occupational prospects, as a means to improve their health status as women.

Effect of menstrual cycle phase on exercise performance of high-altitude native women at 3600 m

At sea level normally menstruating women show increased ventilation (V̇e) and hemodynamic changes due to increased progesterone (P) and estrogen (E2) levels during the mid-luteal (L) compared to the mid-follicular (F) phase of the ovarian cycle. Such changes may affect maximal exercise performance. This repeated-measures, randomized study, conducted at 3600 m, tests the hypothesis that a P-mediated increase in V̇e increases maximal oxygen consumption (V̇O2max) during the L phase relative to the F phase in Bolivian women, either born and raised at high altitude (HA), or resident at HA since early childhood. Subjects (N=30) enrolled in the study were aged 27.7±0.7 years (mean ± s.e.m.) and non-pregnant, non-lactating, relatively sedentary residents of La Paz, Bolivia, who were not using hormonal contraceptives. Mean salivary P levels at the time of the exercise tests were 63.3 pg ml–1 and 22.9 pg ml–1 for the L and F phases, respectively. Subset analyses of submaximal (N=23) and maximal (N=13) exercise responses were conducted only with women showing increased P levels from F to L and, in the latter case, with those also achieving true V̇O2max. Submaximal exercise V̇e and ventilatory equivalents were higher in the L phase (P&lt;0.001). P levels were significantly correlated to the submaximal exercise V̇e (r=0.487, P=0.006). Maximal work output (W) was higher (approximately 5 %) during the L phase (P=0.044), but V̇O2max (l min–1) was unchanged (P=0.063). Post-hoc analyses revealed no significant relationship between changes in P levels and changes in V̇O2max from F to L (P=0.072). In sum, the menstrual cycle phase has relatively modest effects on ventilation, but no effect on V̇O2max of HA native women.

Vaginal bleeding patterns among rural highland Bolivian women: relationship to fecundity and fetal loss

Among the most common reasons given for discontinued use of some contraceptive methods is a disturbance in the menstrual cycle, particularly changes in vaginal bleeding. Work to date suggests marked populational variation in menses duration, but few data have been collected from South America. This longitudinal study of non-contracepting Aymara women (n = 189 providing 837 non-truncated bleeding episodes) identified conceptions and fetal loss via urine tests for human chorionic gonadotropin and classified episodes accordingly to test the hypotheses that (a) vaginal bleeding patterns differ between lactating and non-lactating women, (b) duration of vaginal bleeding accompanying fetal loss differs from that of menstruation, (c) menses preceding a conception are longer than those not followed by a conception. Compared to published values, mean menses duration (3.5 days) in these women was relatively short. Menses duration was not significantly correlated with current age, age at menarche or first birth, parity, time postpartum, or menstrual segment length. Mean menses duration (not preceding a conception) was comparable for lactating and non-lactating women. Mean duration of fetal loss bleeding did not differ from that of menses. Pre-conception episodes were significantly longer than those not followed by conception. Thus, because the rate of conceptions was twice as great among lactating than non-lactating women, the mean duration of all menses (irrespective of conception) was significantly longer in lactating women. Bolivian, and perhaps other South American, women may be particularly disinclined to accept contraceptives (e.g., intrauterine devices) that modify an otherwise relatively brief menses duration. Therefore, a wide variety of contraceptive choices accompanied by population-specific informed counseling is essential. In addition, these findings suggest that studies of fecundability limited to non-lactating women may be biased toward those of relatively lower fecundity and that menses duration may be predictive of risk for some cancers.

The home team advantage: reproduction in women indigenous to high altitude

Although there is substantial evidence that environmental conditions disrupt reproductive function among newcomers to hypoxic settings, it is not certain that low oxygen pressure reduces fertility among those indigenous to high altitude. Even when fertility does appear to be relatively lower, numerous behavioral and sociocultural factors may be responsible. These are best examined within demographic frameworks that delineate a finite list of the proximate determinants of fertility. The findings presented here are based on several studies of indigenous Andean populations (Peruvian Quechua at 4000m, Bolivian Quechua at 3100m, Bolivian Aymara at 4000m). Data on ovarian function suggest that neither progesterone levels nor menstrual cycle length or regularity are significantly different from those of women at lower altitudes. Data on two behavioral factors that determine fertility levels, coital frequency and infant feeding practices, suggest that the former is not likely to be of significance in co-habitating couples, but that variation in breastfeeding patterns has probably made a substantial contribution to differences in fertility among at least some populations at high altitude.

Does hypoxia impair ovarian function in Bolivian women indigenous to high altitude?

Fertility appears to be reduced in at least some high altitude populations relative to their counterparts at lower elevations. Inferring from the difficulties with reproduction of newcomers to high altitude and from animal experiments, it has been hypothesized that this apparent reduction is the result of hypoxia acting to reduce fecundity and/or increase fetal loss. In humans, however, several behavioral as well as biological factors may affect fertility levels. These many factors have been organized by demographers into a framework of seven proximate determinants that includes fecundability (the monthly probability of conception) of which successful ovulation is one component. To test whether ovarian function is impaired in women indigenous to high altitude, we measured salivary progesterone (P) in a sample (n = 20) of Quechua women (aged 19-42 years) residing at 3,100 m. It was found that mean luteal P = 179 pmol/L and mean midluteal P = 243 pmol/L, levels that fall about midway in the range of known values for several populations and are higher than some lower altitude populations. These findings suggest that hypoxia does not appear to significantly impair ovarian function in those with lifelong residence at high altitude. There are, however, several factors common to many high altitude populations that may act to reduce fecundability and fertility including intercourse patterns (affected by marriage and migration practices), prolonged lactation, dietary insufficiency, and hard labor.

Menstrual patterns and fecundity among non-lactating and lactating cycling women in rural highland Bolivia: implications for contraceptive choice

Choosing an appropriate contraceptive method, particularly one based on fertility awareness, depends in part upon the degree of a woman's cycling regularity. However, while the suppressive effect of lactation on ovarian function is well established, the potential influence of continued breastfeeding on menstrual patterns once post-partum cycling has resumed is largely unexamined. This longitudinal study in a population of non-contracepting Aymara women (n = 191 providing 665 non-truncated menstrual segments) identified conceptions and fetal loss via urine tests for hCG and classified segments accordingly to test the hypotheses that (1) cycles in lactating women are significantly different in length and regularity from those of non-lactating women, and (2) cycles in women living at high altitude are significantly different in length and regularity from those at lower altitudes. Analyses found that segments are significantly longer and regularity tends to be less common among lactating than non-lactating women; however, the rate of conception is twice as great among the former than the latter, and the distribution of conception outcomes does not differ between the two groups. Menstrual regularity is not the norm in this population, even among those who are not currently breastfeeding. High altitude per se does not appear to influence menstrual cycling as both regularity and segment length are comparable to other populations, hence women indigenous to high altitude are suitable candidates for a wide variety of contraceptive choices. In addition, these findings suggest that studies of fecundability limited to non-lactating women may be biased towards those of relatively lower fecundity.