Background: Changes in birth seasonality patterns have been documented in several countries, whether long-lasting or temporary. In Spain, a decline in and absence of birth seasonality was reported in 1941–2000. This study extends the analysis to the full period of available monthly data, exploring changes in birth seasonality in Spain, its connection to social/health phenomena, and its related effects. Methods: We analyzed the two available monthly data periods: 1863–1870 and 1900–2021 (n = 73,338,010 births). Fourier spectral analysis and Cosinor analysis were performed to study changes in the overall seasonal pattern. The Chow structural change test analyzed punctual variations. Box-Jenkins time series methodology was applied to estimate the impact of related events on the number of live births. Results: The overall monthly pattern changes, shifting the maximum of births from February in the 19th century to September in the 21st century, experiencing a loss of amplitude. Three structural change points were found in the monthly series of observed/expected births, in 1919, 1940, and 2020, corresponding to the influenza pandemic, the end of the Spanish Civil War, and the Covid-19 lockdown, with temporary impacts on live births of –8.1%, 38.8%, and –16.4%, respectively. Conclusions: The seasonal pattern in Spain has changed substantially in shape and amplitude. While gradual changes appear to be associated with socioeconomic change, there is a clear connection between temporary changes and isolated social/health phenomena. Contribution: We study both gradual and temporary changes in birth seasonality, covering the entire period of data available in Spain, and quantify the effects of related isolated events.

中文翻译：

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西班牙出生季节性的变化：1863年至1870年和1900年至2021年的数据（作者：Adela Recio Alcaide、César Pérez López、Francisco Bolúmar Montrull）

背景：一些国家已经记录了出生季节性模式的变化，无论是长期的还是暂时的。据报道，西班牙 1941 年至 2000 年期间出生季节性下降甚至消失。这项研究将分析扩展到可用月度数据的整个时期，探讨西班牙出生季节性的变化、其与社会/健康现象的联系及其相关影响。方法：我们分析了两个可用的每月数据周期：1863-1870 和 1900-2021（n = 73,338,010 名出生者）。进行傅里叶谱分析和余弦分析来研究整体季节性模式的变化。Chow 结构变化测试分析了准时变化。应用 Box-Jenkins 时间序列方法来估计相关事件对活产数量的影响。结果：总体每月模式发生变化，出生人数最高值从 19 世纪的 2 月转移到 21 世纪的 9 月，出现幅度损失。在 1919 年、1940 年和 2020 年的每月观察/预期出生数据中发现了三个结构性变化点，分别对应于流感大流行、西班牙内战结束和 Covid-19 封锁，对生活产生了暂时影响。出生率分别为 –8.1%、38.8% 和 –16.4%。结论：西班牙的季节模式在形状和幅度上发生了巨大变化。虽然渐进的变化似乎与社会经济变化有关，但临时变化与孤立的社会/健康现象之间存在明显的联系。贡献：我们研究了出生季节性的逐渐变化和暂时变化，涵盖了西班牙可用数据的整个时期，并量化了相关孤立事件的影响。