关键词: 生育周期, 转变模式, 初育年龄, 末育年龄, 生育期长度

Abstract: The reproductive cycle refers to the process from a woman's first to last birth. Through a systematic categorization and analysis of the evolution of reproductive cycles across global regions, combined with theoretical discussions on long-term demographic development, this study reveals that reproductive cycle evolution exhibits significant ergodicity, termed the Reproductive Cycle Transition (RCT). The RCT progresses through four stages: a Steady-State Stage, a Compression Stage, a Leveling-Off Stage, and an Equilibrium Stage. It shifts from a traditional pattern characterized by a low age at first birth, a high age at last birth, and a long reproductive span (“low-high-high”) to a modern pattern characterized by a high age at first birth, a low age at last birth, and a short reproductive span (“high-low-low”). The RCT parallels the fertility transition. Europe, North America, Australia, New Zealand and East Asia have entered the Leveling-Off Stage. In contrast, most of Asia, Africa, and Latin America are in the late stage of the Compression Stage, while East, Central, and West Africa remain in their early stage. China's reproductive cycle exhibits an accelerated pattern, beginning in the 1960s and entering the Leveling-Off Stage by the early 1990s. The shortening of the reproductive span carries the risk of lowest-low fertility. Fertility support policies should target the distinct fertility needs of women across different age groups.

Keywords: Reproductive Cycle, Transition Patterns, Age at First Birth, Age at Last Birth, Reproductive Span