Background: The fertility transition started later in sub-Saharan Africa than in other regions of the world. Moreover, the average number of children per woman declined more slowly there, owing to a distinct mechanism of fertility reduction. It has been argued that the fertility decline in sub-Saharan Africa proceeded through an increase in birth intervals rather than by a limitation of the number of births. Objective: We analyze the fertility transitions in 29 countries to determine which mechanism women resort to in order to reduce their number of children. Methods: Using multiple sample surveys, we estimate and cross-validate trends in parity progression ratios and birth intervals. We identify sub-regional regularities and vanguard trends in the interplay between the dynamics of the lengthening of birth intervals and birth limitation over the period 1962‒2012. Results: While initial fertility declines were driven by a lengthening of birth intervals at all parities, we observe a recent onset of birth limitation in regions and countries that are most advanced in the fertility transition. Conclusions: The experience of sub-Saharan Africa shows that if all parities contribute to the fertility transition from the outset, the main drivers of the fertility decline switch from a lengthening of birth intervals to a limitation of family size when the average fertility reaches about five children per woman. Contribution: Our findings point to the emergence of birth limitation as a new stage in the fertility transition in sub-Saharan Africa. These results have implications for future fertility declines in sub-Saharan Africa.

中文翻译：

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限制生育的出现是撒哈拉以南非洲生育率过渡的新阶段

背景：撒哈拉以南非洲比世界其他地区晚开始了生育过渡。此外，由于生育率下降的独特机制，该地区每名妇女的平均子女人数下降得更为缓慢。有人认为，撒哈拉以南非洲的生育率下降是通过增加生育间隔而不是通过限制出生数量来实现的。目的：我们分析了29个国家的生育率转变，以确定妇女诉诸何种机制以减少子女数量。方法：使用多次抽样调查，我们估计并交叉验证了均等进展率和出生间隔的趋势。我们确定了1962-2012年间生育间隔延长和生育限制的动力学之间相互作用的次区域规律性和先锋趋势。结果：虽然最初的生育率下降是由各个年龄段的生育间隔时间延长导致的，但我们观察到最近在生育率过渡最先进的地区和国家开始出现生育限制。结论：撒哈拉以南非洲的经验表明，如果所有的人均从一开始就促进了生育率的转变，那么当平均生育率达到约5时，生育率下降的主要驱动力便从延长生育间隔转变为限制家庭规模。每个女人的孩子。贡献：我们的研究结果表明，生育限制已成为撒哈拉以南非洲生育率过渡的新阶段。这些结果对撒哈拉以南非洲未来的生育率下降具有影响。