Wearables have the potential to address one of medicine’s major blind spots: the under-representation of women. They could help to close this gap by advancing measurement and monitoring into clinically meaningful insights of personalized data. However, realizing this potential requires validation, equity and clinical rigour to avoid reinforcing existing inequities.

Per- and polyfluoroalkyl substances (PFAS) and psychosocial stress can dysregulate hormonal processes underlying fetal growth. Less is known about the effect of co-exposure to PFAS and stress on birth size. We investigated associations of a preconception mixture of PFAS with birth size and assessed effect modification by perceived stress. We used prospective data from 321 participants from the Study of Environment, Lifestyle, and Fibroids, a cohort of 23-35-year-old women from Detroit, MI who identified as Black/African American. We quantified plasma concentrations of six PFAS in baseline blood samples using online solid-phase extraction-liquid chromatography-isotope dilution tandem mass spectrometry. We assessed experience of perceived stress at baseline using the Perceived Stress Scale-4. Participants reported intervening pregnancies at follow-up visits (at 20, 40, and 60 months). We calculated sex-standardized birthweight-for-gestational-age (BW-for-GA) z-scores from reported birthweight and gestational age at delivery. We employed Bayesian Kernel Machine Regression to estimate associations (βs, with 95

Exposure to metalloids and metals has been associated with childhood cancer, specifically acute leukemia, though studies are limited. During 2020-2023, we conducted a hospital-based case-control study in Italy to evaluate the association between trace element status and childhood leukemia. We enrolled 77 cases with newly-diagnosed acute childhood leukemia and 74 controls referred to the hospital for minor medical procedures. In blood samples collected at hospital admission, we used inductively-coupled plasma mass spectrometry to measure serum concentrations of selenium (and its species), copper, iron, manganese, and cadmium. We estimated odds ratios and 95% confidence intervals using restricted cubic spline regression. Dose-response, confounder-adjusted analyses showed positive monotonic associations of selenium, copper and iron, above a certain level of exposure, with childhood leukemia. Two selenium species, selenoprotein P-bound selenium and selenomethionine, showed similar results to total selenium. Zinc showed an inverse association with leukemia, while there was no appreciable relation with manganese. Copper concentrations in the top tertile were associated with the highest odds ratio of leukemia, though the association was imprecise. These findings indicate the need for further investigation of the potential adverse role of some selenium species and copper in childhood leukemia. However, reverse causation bias and residual confounding could not be ruled out as possible explanations for our findings.

BACKGROUND:Adverse childhood experiences have been associated with several long-term health outcomes, yet their relation to polycystic ovary syndrome-renamed as polyendocrine metabolic ovarian syndrome in 2026-is understudied. Adverse childhood experiences may influence polycystic ovary syndrome risk via disruption of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-gonadal axes. METHODS:We used cross-sectional data to evaluate the association between early life adversities and self-reported polycystic ovary syndrome in Pregnancy Study Online, a North American preconception cohort of females aged 21 to 45 years enrolled during 2013 to 2025. At enrollment, participants completed a baseline questionnaire to ascertain sociodemographics, behavioral factors, and medical history. Thirty days after enrollment, participants completed a supplemental questionnaire that included the Behavioral Risk Factor Surveillance System's 8-item adverse childhood experience module and Brief Trauma Questionnaire. Participants reported physician-diagnosed polycystic ovary syndrome on baseline and follow-up questionnaires during preconception. We fit modified Poisson regression models to estimate prevalence ratios and 95% confidence intervals, adjusting for age, race, ethnicity, childhood financial hardship, and highest level of parental education. We used inverse probability weights to account for supplemental questionnaire nonresponse. RESULTS:Among 10,856 participants, 52% and 26% reported 1 to 3 and ≥4 adverse childhood experiences, respectively; 1169 (10.8%) reported a polycystic ovary syndrome diagnosis. Self-reported polycystic ovary syndrome prevalence ranged from 7.4% (no adverse childhood experiences) to 14.2% (≥4 adverse childhood experiences). Weighted and fully adjusted prevalence ratios for 1 to 3 and ≥4 (vs 0) adverse childhood experiences were 1.33 (95% confidence interval, 1.11-1.60) and 1.64 (95% confidence interval, 1.33-2.01), respectively (per 1-adverse childhood experience increase, prevalence ratio=1.08; 95% confidence interval, 1.05-1.11). Specific adverse childhood experiences associated with the largest increase in polycystic ovary syndrome prevalence included sexual abuse (prevalence ratio=1.82; 95% confidence interval, 1.45-2.29), parental interpersonal violence (prevalence ratio=1.68; 95% confidence interval, 1.29-2.17), emotional abuse (prevalence ratio=1.54; 95% confidence interval, 1.28-1.86), physical abuse (prevalence ratio=1.52; 95% confidence interval, 1.21-1.90), household mental illness (prevalence ratio=1.46; 95% confidence interval, 1.21-1.77), and parental separation/divorce (prevalence ratio=1.43; 95% confidence interval, 1.15-1.77). Results based on Brief Trauma Questionnaire‑derived measures of childhood sexual and physical abuse were consistent with those based on adverse childhood experience measures. CONCLUSION:In this North American cross-sectional study, higher exposure to early life adversities was associated with a higher lifetime prevalence of self-reported physician-diagnosed polycystic ovary syndrome. These findings add to growing evidence that childhood adversities may have lasting effects on gynecologic health and underscore the need for attention to early life stressors in understanding polycystic ovary syndrome.

CONTEXT:Overexposure to the essential trace element selenium has been associated with adverse metabolic and cardiovascular outcomes, hypertension, and diabetes. However, dose-response meta-analyses analyzing the effects of selenium administration on the lipid profile in experimental human studies are lacking. OBJECTIVE:Through a restricted cubic spline regression meta-analysis, the dose-response relation between the dose of selenium administered or blood selenium concentrations at the end of the trials and changes over time in blood lipids, ie, total, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and triglycerides was assessed. DATA SOURCES:Searches were performed on PubMed, Web of Science, Embase, and the Cochrane Library from inception up to January 11, 2025 to identify randomized controlled trials (RCTs) investigating the impact of selenium supplementation on blood lipid profiles among adults. DATA EXTRACTION:A total of 27 eligible RCTs that enrolled healthy individuals, pregnant individuals, and participants with specific health conditions were identified and the relevant data was extracted. DATA ANALYSIS:Dose-response analysis indicated that selenium administration at and above 200 µg/day decreased HDL and LDL cholesterol and increased triglyceride levels. Blood selenium concentrations at the end of the trial above approximately 150 µg/L were positively associated with triglyceride and LDL cholesterol concentrations, and inversely associated with HDL cholesterol. Inorganic selenium supplementation showed stronger associations than organic selenium. At the lowest levels of baseline intake, selenium supplementation appeared instead to have beneficial effects on the lipid profile, with an overall indication of U-shaped curves, apart from HDL-cholesterol. The adverse effects of selenium were stronger in studies involving healthy participants as compared with unhealthy participants and pregnant females, in those having a longer duration of the intervention, particularly more than 3 months, and in European populations at selenium intake levels of above 300 µg/day. CONCLUSIONS:In this dose-response meta-analysis of experimental human studies, an adverse effect of selenium administration on blood lipids at levels around or above the current upper level of intake was observed. SYSTEMATIC REVIEW REGISTRATION:PROSPERO registration No. CRD42022380432.

BACKGROUND:Oil and gas development-a highly prevalent industry in North America-is often located near residential communities. This industry produces a complex mixture of pollutants that may impact human health. Despite well-documented associations between residential proximity to oil and gas development and adverse birth outcomes, no study has examined gestational diabetes mellitus (hereafter, gestational diabetes)-a condition with long-term consequences for maternal-infant health. METHODS:We examined associations between residential proximity to active oil and gas development during pregnancy and gestational diabetes risk by using data from Pregnancy Study Online (PRESTO)-an internet-based preconception cohort study in the USA and Canada. We developed residential proximity measures for active oil and gas development at the estimated date of conception, including distance to the nearest site. For participants whose pregnancy progressed for ≥28 weeks of gestation, we evaluated diagnoses of gestational diabetes via self-administered questionnaires and birth records. We implemented log-binomial regression to estimate risk ratios (RRs) and 95% confidence intervals (CIs), adjusting for covariates, including stratification by pre-pregnancy body mass index (BMI) (<25.0, 25.0-29.9, ≥30.0 kg/m2) and parity (nulliparous, parous). RESULTS:Among 6285 participants, 8.6% of participants reported gestational diabetes. Residence within 5 km of active oil and gas development was not appreciably associated with gestational diabetes (RR: 1.07, 95% CI: 0.81, 1.40) compared with residence ≥20 km away. Associations did not vary by pre-pregnancy BMI or parity. CONCLUSION:We found no consistent evidence of an association between residential proximity to active oil and gas development at conception and the risk of gestational diabetes.

STUDY QUESTION:To what extent is perceived stress during preconception and pregnancy associated with miscarriage incidence? SUMMARY ANSWER:Perceived stress during early pregnancy, but not preconception, was associated with higher miscarriage incidence. WHAT IS KNOWN ALREADY:Some studies have found that higher stress levels are associated with miscarriage risk. However, many of these studies were retrospective, focused on occupational stress only, and/or suffered from under-ascertainment of miscarriage. STUDY DESIGN, SIZE, DURATION:Pregnancy Study Online (PRESTO) is an ongoing prospective preconception cohort study that recruited participants during 2013-2025. Eligible participants were females aged 21-45 years, who resided in the USA or Canada and were trying to conceive without fertility treatments. Eligible partners were males aged ≥21 years. PARTICIPANTS/MATERIALS, SETTING, METHODS:We collected data on perceived stress using the 10-item version of the Perceived Stress Scale (PSS-10) during preconception (every 8 weeks) and early pregnancy for female participants and during preconception only for male participants. We identified pregnancies and miscarriages on bimonthly follow-up questionnaires during preconception and additional questionnaires during early and late pregnancy and postpartum. We fit Cox proportional hazards regression models to estimate hazard ratios (HR) and 95% CIs for the effect of preconception PSS-10 scores (n = 11 189 female and 2656 male participants) and early pregnancy PSS-10 scores (n = 8319 female participants) on miscarriage incidence, adjusting for potential confounders. MAIN RESULTS AND THE ROLE OF CHANCE:About 20% of the pregnancies ended in miscarriage, with the loss occurring at a median of six gestational weeks. Preconception PSS-10 scores in the female or male partner were not appreciably associated with miscarriage incidence. Female PSS-10 scores during gestational weeks 5-8 were strongly associated with higher miscarriage incidence: adjusted HRs for PSS-10 scores of 10-14, 15-19, 20-24, and ≥25 vs <10 in gestational weeks 5-8 were 1.38 (95% CI: 1.07, 1.77), 1.17 (95% CI: 0.89, 1.52), 1.35 (95% CI: 1.00, 1.83), and 2.05 (95% CI: 1.40, 2.99), respectively. In week-specific analyses, an association existed during weeks 4-8 and peaked at week 7. LIMITATIONS, REASONS FOR CAUTION:Our results may be susceptible to reverse causation, unmeasured confounding by nausea and vomiting in pregnancy, and exposure misclassification. WIDER IMPLICATIONS OF THE FINDINGS:Interventions aimed at decreasing stress during early pregnancy may be effective at reducing miscarriage incidence, but confirmation of our results in randomized studies is warranted. STUDY FUNDING/COMPETING INTEREST(S):This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (R01-HD086742, R01-HD105863). Lauren Wise has received in-kind donations for primary data collection in PRESTO from ChartNeo.com. The other authors have no conflicts to report. TRIAL REGISTRATION NUMBER:N/A.

OBJECTIVE:To determine the sensitivity of home pregnancy tests with real-world use by day of testing and cycle length among pregnancy planners who conceived. DESIGN:Pregnancy Study Online (PRESTO, 2018-2024) is an internet-based prospective cohort of pregnancy planners in North America who are not using fertility treatments to conceive. SUBJECTS:We analyzed data from 19,908 pregnancy tests from 5,979 participants who detected a pregnancy with a home pregnancy test. EXPOSURE:Participants reported day-specific information about pregnancy testing and test results from 4 days before expected menses through 4 days after expected menses. Participants also provided the date of their last menstrual period, their most recent menstrual cycle length, and cycle regularity. MAIN OUTCOME MEASURES:We calculated pregnancy test sensitivity by timing of test in relation to expected menstrual period and cycle length. Because most participants did not test daily during the observed window, we imputed missing tests using participants' known test results and binomial distributions specific to the day of testing and cycle length determined by predicted probabilities from generalized linear models on the basis of observed tests. We present the mean probability of a positive test by day of testing and participant-reported cycle length. RESULTS:Median cycle length was 28 days (interquartile range: 27-31 days) and 83.3% of participants reported regular cycles. Among participants with regular cycles, we found a relatively high probability of false negative tests with testing 2, 3, and 4 days before expected menses (12.7%, 21.4%, 46.4%, respectively). The probability of having a positive test increased with cycle day in a supralinear fashion, with over 99% of participants having a positive test by 4 days after the day of expected menses. Longer cycle length was associated with incremental increases in pregnancy test sensitivity, conditional on day of testing. Differences in test sensitivity by cycle length were most pronounced among early testers. CONCLUSION:Real-world estimates of home pregnancy test sensitivity by day of testing and cycle length can empower individuals to make informed decisions about when to start testing. Sensitivity was lower than anticipated before expected menses. For any given day of testing, test sensitivity was higher for individuals with longer menstrual cycle lengths.

BACKGROUND:Cannabis use among reproductive-aged individuals is common, yet there are gaps in our understanding of the effect of cannabis use on adverse birth outcomes. OBJECTIVE:To determine the extent to which female and male preconception cannabis use and female early pregnancy cannabis use are associated with the incidence of preterm birth (PTB), small-for-gestational-age birth (SGA), and large-for-gestational-age (LGA) birth. METHODS:We analysed data from Pregnancy Study Online, an internet-based preconception cohort study of couples trying to conceive. Eligible participants were aged 21-45 years (female) and ≥ 21 years (male) and residents of the United States or Canada. We followed 6838 couples who conceived between June 2013 and September 2024. Both partners completed preconception baseline questionnaires; female participants completed preconception follow-up questionnaires every 8 weeks, at early (< 12 weeks) and late pregnancy (~32 weeks), and at 6 months postpartum. Participants self-reported cannabis use during preconception (female and male) and early pregnancy (female only). We ascertained birthweight and gestational age from birth certificates and questionnaires and defined PTB (delivery < 37 gestational weeks) and SGA and LGA (< 10th and > 90th percentiles of birthweight, respectively, for gestational age and sex). We fit Cox regression models to estimate hazard ratios (HR) and 95% confidence intervals (CI), adjusting for potential confounders. RESULTS:Preconception cannabis use was not appreciably associated with PTB (≥ 1 per week vs. non-use: HR 1.06, 95% CI 0.71, 1.57 for females and HR 1.41, 95% CI 0.73, 2.75 for males). Higher frequency of female cannabis use in early pregnancy was associated with an increased incidence of PTB, although results were imprecise (≥ 1 per week vs. non-use: HR 1.87, 95% CI 1.06, 3.29; < 1/week vs. non-use: HR 0.85, 95% CI 0.36, 2.02). Cannabis use in either partner was not associated with the incidence of SGA or LGA. CONCLUSIONS:Our results support the existing evidence that cannabis use during early pregnancy is a risk factor for PTB.

OBJECTIVE:To identify determinants of selected pregnancy testing behaviors among pregnancy planners and to elucidate the relationship between pregnancy testing and detection. METHODS:In PRESTO (Pregnancy Study Online), a North American prepregnancy cohort study of pregnancy planners (2018-2024), participants reported day-specific information about pregnancy testing spanning 4 days before day of expected menstruation through 4 days after. We used generalized linear models to estimate the association between maternal attributes and pregnancy testing behavior, characterized as the timing of the first test and testing frequency. We used quantile regression to estimate the timing of pregnancy detection among participants who conceived by maternal characteristics and pregnancy testing behavior. We estimated the adjusted risk of having a negative test result and the probability of detecting a very early pregnancy loss by the timing of the pregnancy test. RESULTS:We analyzed data from 20,458 pregnancy tests across 6,569 unique participants. Of the participants, 40.7% of reported they engaged in very early testing , defined as testing more than 4 days before their expected period. We observed a range of pregnancy testing intensity, with some participants testing only once and others testing every day. Among participants who detected pregnancy, very early testers were more than 5 times more likely to have a negative test result before a positive test result than those who waited until the day of expected period to test (adjusted risk ratio [aRR[ 5.89; 95% CI, 4.73-7.33). Very early testers were more than 3 times more likely to have an initial positive test result followed by a negative test result, likely reflecting increased detection of very early pregnancy losses (aRR 3.80; 95% CI, 2.12-6.80). CONCLUSION:Patterns in home pregnancy testing varied widely among pregnancy planners. Early initiation of pregnancy testing was associated with slightly earlier pregnancy detection, but also a marked increase in risk of negative test results and detection of very early pregnancy losses.

In the United States (U.S.), 15% of couples attempting pregnancy experience infertility, and 20% of pregnancies end in miscarriage. Environmental chemical exposures, particularly endocrine-disrupting chemicals (EDCs) from consumer products, may contribute to reproductive health challenges. We mailed wearable passive samplers (Fresh Air wristbands) to 132 female participants across 39 U.S. states and 24 of their male partners in the Pregnancy Study Online (PRESTO) to characterize exposure among couples trying to conceive between January and October 2021. Wristbands were analyzed using thermal desorption gas chromatography-high-resolution mass spectrometry with targeted and nontargeted approaches. Nontargeted analysis revealed exposure to 491 chemicals, predominantly benzenoids (36.9%) and organoheterocyclic compounds (18.3%). Health hazard assessment identified 107 high-risk EDCs and 47 compounds predicted to have medium-to-high impacts on reproductive outcomes, including galaxolide, salicylates, and phthalates. Targeted analysis quantified 43 chemicals, revealing universal exposure to polycyclic aromatic hydrocarbons and phthalates. Lifestyle factors influenced exposures: frequent sunscreen users had up to 3.1 times higher ultraviolet filter exposures, while dog owners had 1.2-2.6 times higher exposure to fragrance compounds. Among cohabitating couples, few similarities were observed, despite shared environments. The findings demonstrate that consumer products contribute to complex exposure mixtures with reproductive health implications during preconception.

BACKGROUND:Dairy intake has been associated with lower fibroid incidence in some studies, but none used standardized serial ultrasound screening to detect fibroids. METHODS:We examined dairy intake and fibroid development in the Study of Environment, Lifestyle and Fibroids, a prospective cohort (2010-2018) of 1,610 Black/African American women with no prior clinical diagnosis of fibroids. At the baseline, participants completed a Food Frequency Questionnaire about their intake of daily milk, cheese, yogurt, and total dairy. At three follow-up visits, conducted approximately every 20 months, participants updated their cow's milk intake. Incident cases were those with ultrasound-detected fibroids among those fibroid-free at the baseline ultrasound. We used Cox proportional hazards models to estimate adjusted hazard ratios for fibroid incidence with 95% confidence intervals (CI). For fibroid growth, we calculated the change in log-volume from one visit to the next. RESULTS:The majority (83%) of participants consumed <0.5 cups of milk/day. Neither dairy nor milk intake was appreciably associated with fibroid incidence. However, the baseline total dairy consumption of ≥1 versus <1 cup/day was associated with a 19% decrease (95% CI = -34%, -0.8%) in fibroid growth over the first 20-month interval. The baseline milk intake of ≥0.5 versus <0.5 cups/day was associated with a 26% decrease in growth (95% CI = -39%, -11%) in the same interval. We did not observe similar associations between time-varying milk intake and growth over other study intervals. CONCLUSIONS:The data from this prospective ultrasound study provide some evidence that dairy intake may reduce fibroid growth.

BACKGROUND:Orgasm can be an important component of sexual wellbeing broadly and specifically in the preconception period, yet epidemiologic research on orgasm is limited. METHODS:We used cross-sectional data from Pregnancy Study Online (PRESTO), a cohort study of females attempting conception with one male partner (N = 6022; 2020-2025), to descriptively evaluate orgasm frequency, its correlates and its relationship to orgasm intensity. We used self-reported data to assess orgasm frequency (Likert scale: never/rarely to always/almost always) and intensity (0-10). Across correlates (e.g. encompassing sociodemographic, medical, behavioral factors), we calculated the absolute difference and 95% confidence interval (CI) in the percentage of participants reporting the highest versus lowest orgasm frequency within levels of each correlate, standardized relative to the difference in the full sample. RESULTS:Over half of the sample reported orgasming 'always', 'almost always' or 'most times' during sexual activity. Partner support was a strong correlate; participants whose partner 'rarely' provided love/affection and emotional support reported less frequent orgasms (standardized percentage-point differences of -11.0, 95% CI -36.7, 14.7 and -27.5, 95% CI -44.4, -10.6, respectively). Irritable bladder syndrome (standardized percentage point difference -15.4, 95% CI -25.5, -5.3), diabetes (standardized percentage point difference -5.8, 95% CI -18.2, 6.7) and depressive symptoms (highest category standardized percentage point difference -11.6, 95% CI -19.3, -4.0) were strong correlates of less frequent orgasms. Participants with lower function on other domains of sexual function reported fewer orgasms. CONCLUSIONS:Important correlates of preconception orgasm frequency spanned relational, clinical and sexual function factors. We discuss implications for conducting etiologic orgasm research.

We estimated the association between redlining, a historic racist practice of mortgage lending discrimination, and fecundability, the per-cycle probability of conception. We analyzed data from 1901 U.S. female participants aged 21-45 years in Pregnancy Study Online (PRESTO; 2013-2023), a prospective preconception cohort study. Participants completed self-administered questionnaires at baseline and every 2 months until conception or 12 months, whichever came first. Using participants' baseline residential addresses, we linked to neighborhoods graded by the U.S. Home Owners' Loan Corporation (HOLC) during the 1930s for perceived riskiness of mortgage lending: A + B (best or still desirable), C (definitely declining), and D (hazardous; ie, redlined). We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% CIs, adjusting for age, calendar year of enrollment, and geographic region of residence. Most participants resided in neighborhoods with riskier grades: 47.1% grade C and 21.7% grade D. Compared with neighborhoods graded A + B, FRs were 0.91 (95% CI, 0.81-1.03) and 0.86 (95% CI, 0.74-1.00) for neighborhoods graded C and D, respectively. In this preconception cohort study, current residence in a historically redlined or declining neighborhood was associated with a moderate decrease in fecundability.

Background: Per- and polyfluoroalkyl substances (PFAS) can disrupt hormonal and metabolic processes that support healthy pregnancy. PFAS exposure has been associated with miscarriage risk, but less is known about exposure to multiple PFAS and psychosocial stress measured at preconception, especially among Black women. Methods: We used prospective data from 538 participants from the Study of Environment, Lifestyle, and Fibroids who self-identified as Black or African American. At baseline (preconception), we measured six PFAS concentrations in plasma samples, and participants completed the Perceived Stress Scale-4 (PSS-4) (higher scores reflect greater stress). Participants reported pregnancy outcomes at follow-up study visits (~20, 40, and 60 months). We used Cox proportional hazards models, with gestational week as the time scale, to estimate adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) characterizing miscarriage risk associated with PFAS concentrations and perceived stress scores. We also used the survival extension of quantile-based g-computation to estimate associations of the mixture (PFAS and perceived stress scores) with miscarriage risk. Results: Ninety-five miscarriages were reported during follow-up. In Cox models, perfluorohexanesulfonic acid was associated with 99% (HR = 1.99, 95% CI = 1.10, 3.58) and 52% (HR = 1.52, 95% CI = 0.73, 3.17) higher miscarriage risk at the 50th–74th and ≥75th percentiles (vs. <50th percentile), respectively. Other PFAS showed little association with miscarriage risk. Perceived stress scores (per 1-standard deviation increase) were associated with 23% (HR = 1.23, 95% CI = 0.98, 1.53) higher miscarriage risk. The mixture was nonlinearly associated with miscarriage risk, but associations were imprecise. Conclusions: Higher perfluorohexanesulfonic acid concentrations and perceived stress scores were associated with miscarriage risk among Black women.

BACKGROUND:Use of chemical hair straighteners ("relaxers") is associated with higher risks of hormonally mediated conditions. We hypothesized users of relaxers would have a higher prevalence of abnormal uterine bleeding (AUB) and dysmenorrhea. MATERIALS AND METHODS:We analyzed baseline data from Pregnancy Study Online, an internet-based preconception cohort study of North American pregnancy planners. We included 14,366 participants aged 21-39 years who enrolled during 2014-2024 and reported on their typical menstrual cycle characteristics when not using hormones. We collected data on history of use, age at first use, frequency per year, duration of use, and number of burns. We defined AUB as cycle length <24 or >38 days, flow ≥ 7 days, irregular cycles, and/or heavy flow (>30 pads/tampons per menses). We defined dysmenorrhea as severe cramps requiring medication and bed rest. We used modified Poisson regression models to estimate prevalence ratios (PRs) and 95% confidence intervals (CIs) for the associations of relaxer use with AUB and dysmenorrhea, adjusted for potential confounders. RESULTS:Overall, 2% of participants were current users and 10% were former users of relaxers. The frequencies of AUB and dysmenorrhea were 31% and 8%, respectively. PRs for current (versus never) relaxer use were 1.16 (95% CI: 1.00-1.33) for AUB and 1.30 (95% CI: 0.94-1.80) for dysmenorrhea. Participants who reported ever experiencing burns (versus never use) had a higher prevalence of dysmenorrhea (1-4 burns: PR = 1.42, 95% CI: 1.04-1.93; ≥5 burns: PR = 1.46, 95% CI: 1.00-2.13). CONCLUSION:Relaxer use was associated with a higher prevalence of menstrual disturbances.