US study finds girls are starting their periods earlier and taking longer to become regular

By Pooja Toshniwal PahariaReviewed by Danielle Ellis, B.Sc.Jun 5 2024

In a recent study published in JAMA Network Open, researchers examined the temporal trends and inequalities in menstruation onset, time to regularity, and the role of early-life body mass index (BMI) as a mediator.

Background

Menarche is the culmination of a sequence of reproductive processes, and early menarche can result in adverse health effects such as cardiovascular disease, cancer, spontaneous abortion, and premature mortality. Studies have documented trends toward early onset of menstruation in the United States (US); however, data on variances based on sociodemographic variables and BMI are scarce.

Most studies concentrate on the average age of menarche, with the frequency of early or late menarche rarely considered. The period from menstruation onset to regular menstrual cycles is an essential but seldom studied part of early-life menstrual health. Longer time to regularity is associated with poorer fertility, longer menstrual cycles, and an increased risk of metabolic disorders and all-cause mortality.

About the study

In the present study, researchers assessed temporal changes in menstruation onset and time taken for regular menstrual cycles in a racially and ethnically diverse sample group born between 1950 and 2005. They examined general temporal patterns and whether they differed by sociodemographic characteristics. They also investigated whether BMI at menarche would explain the observed temporal patterns.

The research included participants from the current Apple Women's Health research from 4 November 2019 to 20 March 2023. Eligible participants had menstruated at least once throughout their lives, lived in the United States, were at least 18 years old, could speak in English, and were the only users of an iCloud account and an iPhone. Upon enrollment, individuals completed demographic, reproductive, and medical history questions.

The study exposure was the birth year of the participants. The primary outcomes included the age of menstruation onset and time taken for regular menstrual cycles, which the participants reported. The researchers classified age at menarche as early menarche (before 11 years of age), very early menarche (before nine years of age), and late menarche (after 16 years of age). They classified the period of regularity as two years or less, three to four years, more than five years, not yet regular, or regular following hormone therapy.

The BMI z-scores were derived using the Centers for Disease Control and Prevention's growth charts. They also performed an exploratory causal mediation analysis to determine the proportions of temporal trends in menarche regularity mediated by BMI z-scores at menarche. They used extended linear regressions and multinomial logistic regressions to conduct their investigation. Covariates in the study were race, ethnicity, subjective socioeconomic position (SES), and geographic location. SES was measured using the MacArthur Scale of Subjective Social Status.

Results

Among 71,341 females, the mean age at menstruation onset was 12 years; 2,228 (3.0%) were Asian, 3,665 (5.0%) were non-Hispanic Blacks, 49,518 (69.0%) were non-Hispanic Whites, 4,918 (7.0%) were Hispanic, and 8,461 (12%) belonged to other races and ethnicities). Among the participants, 5,223 took birth in the 1950-1969 period, 12,226 births occurred in the 1970-1979 period, 22,086 births occurred in the 1980-1989 period, 23,894 births occurred in the 1990 -1999 period, and 7,912 births were reported in the 2000-2005 period.

The mean participant age at menstruation onset fell from 13 years among those born between 1950 and 1969 to 12 years among those with births reported between 2000 and 2005. The count of females with early menstruation onset rose from 449 (9.0%) to 1,223 (16%), while those experiencing extremely early menarche elevated from 31 females (0.60%) to 110 females (1.40%). Females reporting late menarche fell from 286 (6.0%) to 137 (2.0%).

Among 61,932 individuals with time to regular menstrual cycles, the number attaining regularity within two years fell from 3,463 (76%) to 4,075 (56%), while the number with not yet attained menstrual regularity rose from 153 (three percent) to 1,375 (19%).

The amplitude of the temporal trend toward menarche at an earlier age was pronounced among Asians, non-Hispanic Blacks, or other races (compared to non-Hispanic Whites) and those from low socioeconomic backgrounds. In a subgroup of 9,865 individuals with available BMI data at menstruation onset, the mediation analysis revealed that BMI explained 46% of the trends observed at the onset of menstruation.

Conclusion

The study findings showed that as birth years increase, menarche age decreases and time to regular menstrual cycles increases, especially among non-Hispanic Blacks, Asians, or those of mixed races (as compared to non-Hispanic Whites) and those with low socioeconomic levels. These trends might contribute to poorer health outcomes and inequities in the United States.

The study underlines the importance of future research into post-menarche years, early intervention, and the impact of BMI and other variables on reproductive development. It also advocates for greater awareness among healthcare professionals and researchers.