Importance: Early menarche is associated with adverse health outcomes. Trends toward earlier menarche have been observed in the US, but data remain limited on differences by sociodemographic factors and body mass index (BMI). Time from menarche to cycle regularity is another understudied early-life characteristic with health implications.Objectives: To evaluate the temporal trends and disparities in menarche and time to regularity and explore early-life BMI as a mediator.Design, Setting, and Participants: This ongoing cohort study enrolled participants from an ongoing mobile application–based US cohort from November 14, 2019, to March 20, 2023.Exposures: Birth year (categorized as 1950-1969, 1970-1979, 1980-1989, 1990-1999, and 2000-2005).Main Outcomes and Measures: Main outcomes were age at menarche and time to regularity, which were self-recalled at enrollment. In addition, early (aged <11 years), very early (aged <9 years), and late (aged ≥16 years) age at menarche was assessed.Results: Among the 71 341 female individuals who were analyzed (mean [SD] age at menarche, 12.2 [1.6] years; 2228 [3.1%] Asian, 3665 [5.1%] non-Hispanic Black, 4918 [6.9%] Hispanic, 49 518 [69.4%] non-Hispanic White, and 8461 [11.9%] other or multiple races or ethnicities), 5223 were born in 1950 to 1969, 12 226 in 1970 to 1979, 22 086 in 1980 to 1989, 23 894 in 1990 to 1999, and 7912 in 2000 to 2005. The mean (SD) age at menarche decreased from 12.5 (1.6) years in 1950 to 1969 to 11.9 (1.5) years in 2000 to 2005. The percentage of individuals experiencing early menarche increased from 449 (8.6%) to 1223 (15.5%), the percentage of individuals experiencing very early menarche increased from 31 (0.6%) to 110 (1.4%), and the percentage of individuals experiencing late menarche decreased from 286 (5.5%) to 137 (1.7%). For 61 932 participants with reported time to regularity, the percentage reaching regularity within 2 years decreased from 3463 (76.3%) to 4075 (56.0%), and the percentage not yet in regular cycles increased from 153 (3.4%) to 1375 (18.9%). The magnitude of the trend toward earlier menarche was greater among participants who self-identified as Asian, non-Hispanic Black, or other or multiple races (vs non-Hispanic White) (P = .003 for interaction) and among participants self-rated with low (vs high) socioeconomic status (P < .001 for interaction). Within a subset of 9865 participants with data on BMI at menarche, exploratory mediation analysis estimated that 46% (95% CI, 35%-61%) of the temporal trend in age at menarche was explained by BMI.Conclusions and Relevance: In this cohort study of 71 341 individuals in the US, as birth year increased, mean age at menarche decreased and time to regularity increased. The trends were stronger among racial and ethnic minority groups and individuals of low self-rated socioeconomic status. These trends may contribute to the increase in adverse health outcomes and disparities in the US.

The menstrual cycle is an important vital sign beginning in early life.¹ Irregular cycles have been associated with adverse health outcomes.² Polycystic ovary syndrome (PCOS), characterized by irregular cycles and hyperandrogenism, is a common ovulatory disorder affecting 8% to 13% of reproductive-aged females (15-49 years),^3,4 but not all individuals with irregular cycles are diagnosed with PCOS (due to underdiagnosis or other etiologies such as hypothalamic amenorrhea).^5-8

Using menstrual products is a part of managing menstrual bleeding. Product use may represent individual, social, and economic influences. A few studies on menstrual product use from specific regions in the United States reported differences in use across demographic factors like age and race and ethnicity. To evaluate menstrual product use patterns and how they vary by sociodemographic, health, and menstrual characteristics in a large US cohort. We used data from 11,455 participants across the United States from the Apple Women's Health Study, an ongoing mobile application-based US cohort, who provided consent, enrolled between November 2019 and January 2024, and responded to relevant surveys. Data included age, race and ethnicity, ancestry, gender identity, socioeconomic status, gynecological conditions, menstrual characteristics, use of menstrual products (panty liners, sanitary napkins or pads, regular tampons, super-absorbent tampons, a combination of pads or tampons but not used together, internal cup menstrual collection device, period underwear, or other), and whether sleeping with a tampon among tampon users. We obtained the percentages and 95% confidence intervals of each product use, overall and by several characteristics. We used chi-square tests and 95% confidence intervals to compare percentages across categorical characteristics. Overall, the prevalence of regular tampons use was 48%, followed by pads (47%), panty liners (43%), super-absorbent tampons (36%), period underwear (20%), cups (18%), a combination of pads or tampons but not used together (18%), other products (2%), and no product (4%). Among tampon users, 61% sleep with a tampon. Compared to individuals aged 30 to 39 years, those aged <20 years were more likely to use pads (57% [95% confidence interval: 53-61] vs 45% [95% confidence interval: 43-46]) and less likely to use cups (12% [95% confidence interval: 10-15] vs 21% [95% confidence interval: 19-22]) or period underwear (17% [95% confidence interval: 14-20] vs 22% [95% confidence interval: 21-23]), and those aged ≥50 years were less likely to use regular tampons (32% [95% confidence interval: 28-36] vs 50% [95% confidence interval: 48-52]). Compared to non-Hispanic White participants, those who self-identified as Asian, Hispanic, or non-Hispanic Black were less likely to use tampons (37% [95% confidence interval: 31-42], 39% [95% confidence interval: 36-43], 31% [95% confidence interval: 27-35] vs 50% [95% confidence interval: 49-51]); Asian or Hispanic individuals were less likely to use cups (15% [95% confidence interval: 11-18], 15% [95% confidence interval: 13-17] vs 19% [95% confidence interval: 18-20]). Compared to those with high socioeconomic status, participants with lower socioeconomic status used pads more frequently (50% [95% confidence interval: 48-52] vs 42% [95% confidence interval: 41-44]). Compared to those without any gynecological conditions, those with endometriosis were more likely to use super-absorbent tampons (38% [95% confidence interval: 35-41] vs 33% [95% confidence interval: 32-35]). Those with longer bleed days used pads more often than those with shorter bleed days; similar patterns were seen for super-absorbent tampons or period underwear (P values < .05). In this cohort, tampons and pads were reported with high frequency, in contrast to the low frequency for period underwear/cups. Use differed by sociodemographic, health, and menstrual characteristics. Our findings provide insights into menstrual product use among US adults, informing discussions among clinicians, policymakers, and patients regarding menstrual management.

Per- and polyfluoroalkyl substances (PFAS) may impact ovarian folliculogenesis and steroidogenesis, but whether prenatal exposure may impact offspring reproductive health is unknown. This study examines the extent to which maternal PFAS plasma concentrations during pregnancy are associated with polycystic ovary syndrome (PCOS) and related characteristics in female offspring. We studied 322 mother-daughter pairs in Project Viva, a Boston-area longitudinal pre-birth cohort enrolled 1999-2002. We examined associations of maternal prenatal (median: 9.6 weeks gestation) plasma concentrations of six PFAS (log2 transformed) with PCOS and related characteristics among daughters during mid-to-late adolescence. We estimated the associations of single PFAS and PFAS as a mixture with each outcome, using logistic regression and quantile g-computation, respectively, adjusting for parity, and maternal sociodemographic and other lifestyle/health factors. Among the 322 mother-daughter pairs, the majority of mothers identified as non-Hispanic White and had a college degree, and 13% of daughters had either self-reported PCOS or probable PCOS based on irregular menstrual cycles and clinical or biochemical markers of hyperandrogenism. Among all daughters, there were 27% with irregular menstrual cycles, 34% with hirsutism, and 6% with moderate-to-severe acne. When fully adjusted for confounders, per doubling of maternal 2-(N-ethyl-perfluorooctane sulfonamido) acetate (EtFOSAA) concentration was associated with higher odds of self-reported PCOS [OR (95% CI) = 2.66 (1.18, 5.99)], and per doubling of maternal perfluorononanoate (PFNA) concentration was associated with higher odds of moderate-to-severe acne [OR (95% CI) = 2.33 (1.09, 4.99)] in daughters with or without irregular menstrual cycles. We found no associations of the mixture of six PFAS with PCOS or related traits. Our findings suggest a positive association between maternal concentrations of EtFOSAA and PCOS in their daughters during mid-to-late adolescence, although future studies with larger sample size and extended follow-up across the reproductive life-course are needed.

Background: Associations between early‐life menstrual cycle characteristics (MCC) and gestational diabetes (GDM) remain unclear.Objectives: To evaluate associations between early‐life MCCs and GDM in first pregnancy, across pregnancies and its recurrence.Methods: This analysis included participants from a US‐based digital cohort enrolled between 11/2019 and 9/2023 who provided consent, completed relevant surveys, were without diabetes and aged ≥18 at first pregnancy (n = 30,473). Age at menarche [<11 (early), 11–15 (referent), ≥16 (late) years] and time from menarche to cycle regularity [<1 (referent), 1–2, 3–4, ≥5 years, not yet regular, regular after hormones] were self‐recalled at enrolment. Additionally, the last three categories were considered prolonged time‐to‐regularity (PTTR). GDM history was recalled at enrolment for each pregnancy. We restricted to pregnancies of ≥24 weeks with a live birth. We evaluated associations of early‐life MCCs with GDM at first pregnancy using modified Poisson regression, across pregnancies using cluster‐weighted Poisson generalised estimating equation and GDM recurrence using multinomial logistic regression, adjusted for sociodemographic, early‐life factors and age at pregnancy. Missing variables were imputed with multiple imputation by chained equations.Results: Among 30,473 participants, 20,591 had eligible first pregnancies, of which 5.9% reported GDM. In 17,512 participants with ≥2 pregnancies, 8.3% had GDM once and 3.7% had recurrent GDM. Early menarche (<11 years, vs. 11–15 years) was associated with GDM in first pregnancy (RR 1.34, 95% CI 1.15, 1.57), across pregnancies (RR 1.24, 95% CI 1.10, 1.39) and recurrence (OR 1.51, 95% CI 1.21, 1.89). PTTR was associated with GDM in the first pregnancy (RR 1.22, 95% CI 1.08, 1.38), across pregnancies (RR 1.16, 95% CI 1.05, 1.27) and recurrence (OR 1.19, 95% CI 0.99, 1.43).Conclusions: Earlier menarche and prolonged time‐to‐regularity are associated with higher risk of GDM and recurrence, suggesting menstrual characteristics during childhood/adolescence as potential early‐life markers for GDM.