International variability in ages at menarche, first livebirth, and menopause

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 an d the timing between these events among different populations of the world. This study describes the variability in reproductive factors across popula tions in Europe, the Americas, Asia, Australia, and Africa. The study sampl e consisted of 18,997 women from 13 centers in 11 countries interviewed bet ween 1979 and 1988 who comprised the control group in a World Health Organi zation international, multicenter case-control study of female cancers. All were surveyed with the same questionnaire and methodology. Overall, a typi cal 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 men arche varied across centers from 13 to 16 years. For all centers, the media n age at first livebirth was 20 or more years, with the largest observed me dian (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, youn ger women had a first birth at a later age than did older women. This tende ncy was more accentuated in some populations. These results reveal, perhaps for the first time, the variability of reproductive histories across diffe rent populations in a large variety of geographic and cultural settings. Ex cept for menopause, international variability is substantial for both biolo gically related variables (age at menarche) and culturally related variable s (age at first birth). There is a generational effect, characterized by mo re variability of age at first birth and delay to first birth in the younge r than in the older generations.