International variability in ages at menarche, first livebirth, and menopause. World Health Organization Collaborative Study of Neoplasia and Steroid Contraceptives.

The occurrences and timing of reproduction-related events, such as menarche, first birth, and menopause, play major roles in a woman's life. There is a lack of comparative information on the overall patterns of the ages at and the timing between these events among different populations of the world. This study describes the variability in reproductive factors across populations in Europe, the Americas, Asia, Australia, and Africa. The study sample consisted of 18,997 women from 13 centers in 11 countries interviewed between 1979 and 1988 who comprised the control group in a World Health Organization international, multicenter case-control study of female cancers. All were surveyed with the same questionnaire and methodology. Overall, a typical woman in this study reached menarche at age 14 years and delivered her first live child 8 years later, at age 22. She was 50 years old at natural menopause and had had 36 years of reproductive life. The median ages at menarche varied across centers from 13 to 16 years. For all centers, the median age at first livebirth was 20 or more years, with the largest observed median (25 years) occurring in China. The median delay from menarche to first livebirth ranged from 5 to 11 years. Among the centers, the median age at natural menopause ranged between 49 and 52 years. In most populations, younger women had a first birth at a later age than did older women. This tendency was more accentuated in some populations. These results reveal, perhaps for the first time, the variability of reproductive histories across different populations in a large variety of geographic and cultural settings. Except for menopause, international variability is substantial for both biologically related variables (age at menarche) and culturally related variables (age at first birth). There is a generational effect, characterized by more variability of age at first birth and delay to first birth in the younger than in the older generations.