Early and Irregular Periods Are Rising Among Young Women

Young women, especially those from racial and ethnic minority groups and lower socioeconomic statuses, are experiencing their first periods earlier and taking longer to reach regularity compared to past generations, according to a study published in JAMA Network Open.

Menarche, as referred to by study researchers, is when a girl gets her first period, marking the start of reproductive maturity.

If the first period happens early, it can increase the risk of health issues like heart disease, cancers, and early death, the study noted. Late menarche could lead to a higher chance of bone fractures.

Over the last 50 years, girls in the United States and worldwide have been getting their periods earlier, often influenced by factors like race, ethnicity and socioeconomic status.

Studies have shown mixed results on these trends, but one common factor is obesity, which has been rising in children and is linked to early puberty.

However, it's unclear if obesity is the main cause. Another important aspect is the time it takes for periods to become regular after menarche, as irregular cycles can indicate health risks.

Although this subject has been studied in Japan and France, this trend hasn't been fully explored in the U.S.

To understand the differences in when young women get their first period and how long it takes for their periods to become regular, researchers studied participants in the ongoing U.S. Apple Women's Health cohort study.

This study included users of the Apple Research app on their iPhones who had ever had a period and were at least 18 years old.

Participants also included girls who started their periods early (before age 11), very early (before age 9) and late (at age 16 or older).

The participants were grouped by birth year: 1950-1969, 1970-1979, 1980-1989, 1990-1999 and 2000-2005. The study is still ongoing, but data was collected from participants who enrolled between November 2019 and March 2023.

The study asked participants when they had their first period, with options ranging from "7 years old or younger" to "16 years old or older." Those who didn’t know or preferred not to answer were excluded.

The the age of the first period was looked at as well as how long it took for participant’s periods to become regular, with options from "less than a year" to "more than 5 years" or "still not regular."

The study considered factors like race, ethnicity, socioeconomic status, and geographic location.

For some participants, the researchers also looked at their body mass index (BMI) at the time of their first period to see if it influenced the timing or regularity of their menstrual cycles.

Among the 71,341 females born between 1950 and 2005, it was found that the average age of a girl’s first period decreased from 12.5 years in 1950-1969 to 11.9 years in 2000-2005.

Early menarche cases increased from 8.6% to 15.5%, while very early menarche cases rose from 0.6% to 1.4%. Late menarche cases dropped from 5.5% to 1.7%.

Fewer girls achieved regular cycles within two years, decreasing from 76.3% to 56.0%, and those not yet regular increased from 3.4% to 18.9%.

The trend was more pronounced among Asians, non-Hispanic Blacks and those of multiple races, as well as those with lower socioeconomic status.

BMI accounted for 46% of the trend toward earlier menarche.

Overall, this study included its strengths and limitations.

Strengths include the large sample size of over 70,000 women of different backgrounds, which helped identify differences among racial and ethnic groups.

The study also examined trends over time in early or late first periods, not just the average age.

In addition, this is the first study to report the time to regular periods is getting longer, suggesting new research directions. The study also used digital data to check if BMI at first period affects these trends.

Limitations include the request of self-reporting on participants remembering their past, which could lead to unclear results. BMI data was also only available for a number of participants.

Further, researchers didn’t consider other early-life factors that could influence the trends, and results may not apply to all women in the U.S.

Based on results, researchers suggest that further awareness among healthcare practitioners are researchers is crucial to understand the reasons for these trends.