Long-term trends in the incidence of endometriosis in China from 1990 to 2019: a joinpoint and age-period-cohort analysis.

BACKGROUND: Trends in the incidence of endometriosis in China remain unknown. The purpose of this study was to examine the trends in the incidence of endometriosis and the effects of age, period, and cohort on them. METHODS: Trends in endometriosis incidence were estimated using joinpoint regression. Age-period-cohort analysis was used to analyze the effects of age, period, and cohort on these trends. Endometriosis incidences in China (1990-2019) were retrieved from the Global Burden of Disease Study 2019. Annual percentage change and average annual percent change (AAPC) were analyzed by joinpoint regression, and relative risks were analyzed using an age-period-cohort model. RESULTS: Age-standardized incidence rates (ASIRs) declined between 1990 and 2019 in China, with an overall AAPC of -1.2% (95% CI: -1.20, -1.10). Compared to 1990, the ASIR in 2019 decreased by almost 30%. Moreover, the joinpoint regression analysis revealed that endometriosis ASIRs showed a downward trend across all age groups. A significant age-related effect was seen for endometriosis incidence among young women aged 15-24 years, which then decreased with advancing age. Consistently, the effect of the period on endometriosis incidence showed a declining trend, and the effect of birth cohort decreased by 0.53 (42.7%) from 1938-1942 to 1998-2002. CONCLUSIONS: Endometriosis ASIRs declined from 1990 to 2019. The effects of period and birth cohort on endometriosis incidence exhibited a declining trend across all age groups. The effect of age on endometriosis incidence showed an increasing trend before the age of 24, followed by a decreasing trend with subsequent advancing age.