U.S. Girls Got Their First Periods Increasingly Earlier Over the Last 50 Years, New Study Finds

Trend is especially pronounced among Black, Hispanic and Asian participants, and those who report lower socioeconomic status

Girls in the United States had their first periods earlier over the last five decades and it took longer to experience regular cycles, a new study has found.

The study, published in JAMA Network Open, found the trend is especially pronounced among Black, Hispanic, Asian and mixed race participants, and among those who reported lower socioeconomic status.

“This is important because early menarche,” or a first period, “and irregular periods can signal physical and psychosocial problems later in life,” said Zifan Wang, a postdoctoral research fellow at Harvard University’s TH Chan School of Public Health and lead author of the study.

Beginning in 2019, researchers from Harvard and the National Institute of Environmental Health Sciences (NIEHS) surveyed more than 71,000 participants born between 1950 and 2005 about when they got their first period, when it became regular and for certain demographic information. Researchers then divided the group into five generational brackets.

They found that women born in the oldest bracket, between 1950-1969, got their period at 12.5 years old on average, compared to 11.9 years old for the youngest group, born between 2000-2005.

The study was conducted through an app as part of the Apple Women’s Health Study. This has allowed researchers to check back in with a group multiple times, or what researchers call a longitudinal study design.