Objective: To describe the secular trends of age at menarche and age at natural menopause of women from a county of Shandong Province.
Methods: Based on the data of the Premarital Medical Examination and the Cervical Cancer and Breast Cancer Screening of the county, the secular trends of age at menarche in women born in 1951 to 1998 and age at menopause in women born in 1951 to 1975 were studied. Joinpoint regression was used to identify potential inflection points regarding the trend of age at menarche. Average hazard ratios (AHR) of early menopause among women born in different generations were estimated by performing multivariate weighted Cox regression.
Results: The average age at menarche was (16.43±1.89) years for women born in 1951 and (13.99±1.22) years for women born in 1998. The average age at menarche was lower for urban women than that for rural women, and the higher the education level, the lower the average age at menarche. Joinpoint regression analysis identified three inflection points: 1959, 1973 and 1993. The average age at menarche decreased annually by 0.03 (P < 0.001), 0.08 (P < 0.001), and 0.03 (P < 0.001) years respectively for women born during 1951-1959, 1960-1973, and 1974-1993, while it remained stable for those born during 1994-1998 (P=0.968). As for age at menopause, compared with women born during 1951-1960, those born during 1961-1965, 1966-1970 and 1971-1975 showed a gradual decrease in the risk of early menopause and a tendency to delay the age at menopause. The stratified analysis presented that the risk of early menopause gradually decreased and the age of menopause showed a significant delay among those with education level of junior high school and below, but this trend was not obvious among those with education level of senior high school and above, where the risk of early menopause decreased and then increased among those with education level of college and above, and the corresponding AHRs were 0.90 (0.66-1.22), 1.07 (0.79-1.44) and 1.14 (0.79-1.66).
Conclusion: The age at menarche for women born since 1951 gradually declined until 1994 and leveled off, with a decrease of nearly 2.5 years in these years. The age at menopause for women born between 1951 and 1975 was generally delayed over time, but the trend of first increase and then decrease was observed among those with relatively higher education levels. In the context of the increasing delay in age at marriage and childbearing and the decline of fertility, this study highlights the necessity of the assessment and monitoring of women' s basic reproductive health status, especially the risk of early menopause.
目的: 描述中国山东某县女性初潮年龄与绝经年龄长期趋势。
方法: 应用研究地区婚前医学检查及宫颈癌和乳腺癌筛查资料，研究1951—1998年出生女性月经初潮年龄及1951—1975年出生女性绝经年龄长期变化趋势。采用Joinpoint回归确定初潮年龄长期趋势有无拐点以及拐点年份，采用多因素加权Cox回归估计不同年代出生女性较早绝经平均风险比(average hazard ratios，AHR)。
结果: 1951年和1998年出生女性平均初潮年龄分别为(16.43±1.89)岁和(13.99±1.22)岁，城镇女性低于农村女性，教育水平越高女性平均初潮年龄越低；Joinpoint回归发现1959年、1973年和1993年三个拐点年份，1951—1959年、1960—1973年和1974—1993年出生者初潮年龄分别年均减小0.03岁(P < 0.001)、0.08岁(P < 0.001)和0.03岁(P < 0.001)，1994—1998年出生者初潮年龄维持平稳(P=0.968)。与1951—1960年出生女性相比，1961—1965年、1966—1970年和1971—1975年出生者较早绝经风险总体上逐渐降低，绝经年龄呈现延迟趋势；分层分析显示，教育水平为初中及以下者较早绝经风险逐渐降低，绝经年龄呈现明显延迟趋势，但教育水平为高中及以上者这一趋势并不明显，其中教育水平为大专及以上者较早绝经风险先降后升，相应的AHR依次为0.90(0.66~1.22)、1.07(0.79~1.44)和1.14(0.79~1.66)。
结论: 1951年以来出生女性初潮年龄逐渐下降，至1994年趋于平稳，40余年下降近2.5岁；1951—1975年出生女性绝经年龄总体上随时间推移而延迟，但教育水平相对较高人群呈现先延迟而后提前的趋势。在婚育年龄推迟与人群生育力下降的双重背景下，应加强女性基础生殖健康状况尤其是较早绝经风险的评估与监测。
Keywords: Age; Menarche; Menopause; Reproductive health; Women' s health.