Temporal trends in age at menarche and age at menopause: a population study of 312 656 women in Norway

Abstract

STUDY QUESTION Have mean age at menarche or mean age at natural menopause changed from the 1939 birth cohort to the 1964 birth cohort? SUMMARY ANSWER We estimated a minor decrease in mean age at menarche and an increase by nearly 3 years in mean age at natural menopause. WHAT IS KNOWN ALREADY In the Western world, age at menarche decreased across birth cohorts from the early 1800s until the 1950s. Whether mean age at menarche has continued to decrease in birth cohorts after the 1950s remains uncertain. It is also uncertain whether mean age at natural menopause has changed across birth cohorts. STUDY DESIGN, SIZE, DURATION We performed a retrospective population study of 312 656 women who were born in Norway during the years 1936–1964. PARTICIPANTS/MATERIALS, SETTING, METHODS The data were obtained by two self-administered questionnaires from women who participated in the Norwegian breast cancer screening program (BreastScreen Norway) during the years 2006–2014. We used flexible parametric survival models with restricted cubic splines to estimate mean age at menarche, mean age at menopause and mean number of years between menarche and menopause according to the women’s year of birth. The women who were still having menstrual periods contributed with follow-up time until the time of data collection, and the women who had reported surgical removal of the uterus and/or both ovaries prior to natural menopause contributed with follow-up time until the time of surgery. MAIN RESULTS AND THE ROLE OF CHANCE The mean age at menarche was 13.42 years (95% CI: 13.40–13.44 years) among women born during 1936–1939, and it was 13.24 years (95% CI: 13.22–13.25 years) among women born during 1960–1964. The mean age at natural menopause increased from 50.31 years (95% CI: 50.25–50.37 years) among women born during 1936–1939 to 52.73 years (95% CI: 52.64–52.82 years) among women born during 1960–1964. The mean number of years between menarche and menopause increased from 36.83 years (95% CI: 36.77–36.89 years) to 40.22 years (95% CI: 40.11–40.34 years). LIMITATIONS, REASONS FOR CAUTION Information about age at menarche and age at menopause was based on self-reports. WIDER IMPLICATIONS OF THE FINDINGS Late menopause is associated with increased risk of breast cancer but also with increased life expectancy. Thus, higher mean age at menopause may partly explain the increase in breast cancer incidence after menopause and the increase in life expectancy in recent time. Also, a longer interval between menarche and menopause could suggest that the number of years of female fecundity has increased. STUDY FUNDING/COMPETING INTEREST(S) This work was funded by the South-Eastern Norway Regional Health Authority [grant number 2016112 to M.S.G.] and by the Norwegian Cancer Society [grant number 6863294-2015 to E.K.B.]. The authors declare no conflicts of interest.

Ultrasound assessment of pubertal breast development in girls: intra- and interobserver agreement

“…The age at menarche declined between the 19th century and the first half of the 20th century in Western countries (57)(58)(59)(60). In Norway, the menarcheal age fell from above 15.6 years for women born around 1850 to about 13.3 years for women born after 1940 (58) and has been stable at around 13 years since then (61)(62)(63)(64)(65)(66). This finding is consistent with trends in other European countries (27,30,31,67).…”

“…Compared to the current pubertal references used in Norway based on Danish data from 1991-1993, our estimated ages at onset for breast (B2) and pubic hair development (PH2) and menarche were advanced by 0.5, 0.4 and 0.7 years (27), respectively ( Table 5). The Tanner B3 and B4 stages occurred 0.9 and 0.8 years earlier (27) (66). When reviewing the published ages at menarche in Norway, our estimate for girls with a known Norwegian origin (mean age: 13.1 years) was still in the lower range compared to previous estimates ( Figure 5).…”

“…However, larger population-based studies following similar designs and conducted in different geographical areas within Norway should be carried out to explore how the trend of pubertal timing develops in Norway. (58,65,66,78,(187)(188)(189)(190)(191)(192)(193)(194). Open markers are retrospective surveys in adult women.…”

Understanding diffusion‐weighted MRI analysis: Repeatability and performance of diffusion models in a benign breast lesion cohort

“…In general, the cohort is taken to be premenopausal from population statistics. 47 Longer term repeatability will also reflect the instability of scanner performance, as well as changes arising from hardware or software. In this study, the effect of specific acquisition parameters on repeatability was not considered, but the chosen protocol is a realistic reflection of clinical DWI protocols and so presents a fair indication of expected CoVs.…”

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“…However, a population study of 312,656 women born in Norway between 1936 and 1964 has found that their mean age at natural menopause did indeed increase – by more than two years over the study period, rising from 50.31 years in those born during 1936–1939 to 52.73 years in those born during 1960–1964. 3…”