Department of Health, Society, and Behavior, and the Center for Population, Inequality, and Policy, University of California, Irvine, California, USA.
Program in Public Health, University of California, Irvine, California, USA.
Am J Hum Biol. 2023 Mar;35(3):e23830. doi: 10.1002/ajhb.23830. Epub 2022 Nov 5.
We aim to contribute to the literature reporting tests of selection in utero. The theory of reproductive suppression predicts that natural selection would conserve mechanisms, referred to collectively as selection in utero, that spontaneously abort fetuses unlikely to thrive as infants in the prevailing environment. Tests of this prediction include reports that women give birth to fewer than expected male twins, historically among the frailest of infants, during stressful times. The onset of the COVID-19 pandemic in the United States in Spring 2020 demonstrably stressed the population. We test the hypothesis that conception cohorts in gestation at the onset of the pandemic in the United States yielded fewer than expected live male twin births.
We retrieved deidentified data on the universe of live births in the United States from the National Center for Health Statistics birth certificate records. We applied Box-Jenkins time-series methods to the twin secondary sex ratio computed for 77 monthly conception cohorts spanning August 2013 to December 2019 to detect outlying cohorts in gestation at the onset of the pandemic.
The twin secondary sex ratio fell below expected values in three conception cohorts (i.e., July, September, and October 2019, all p < .05) exposed in utero to the onset of the pandemic.
Our results add to prior findings consistent with selection in utero. The role of selection in utero in shaping the characteristics of live births cohorts, especially during the COVID-19 pandemic, warrants further scrutiny.
我们旨在为报道宫内选择检测的文献做出贡献。生殖抑制理论预测，自然选择将保留各种机制，这些机制统称为宫内选择，这些机制会自发地中止在当前环境中不太可能茁壮成长为婴儿的胎儿。对这一预测的检验包括报告称，在压力时期，女性生育的男性双胞胎数量低于预期，而男性双胞胎历来是婴儿中最脆弱的群体之一。2020 年春季，美国 COVID-19 大流行的爆发明显给人口带来了压力。我们检验了这样一个假设，即在 COVID-19 大流行在美国开始时妊娠的受孕队列生育的活男婴数量低于预期。
我们从国家卫生统计中心的出生证明记录中检索了美国所有活产儿的数据，这些数据是匿名的。我们应用 Box-Jenkins 时间序列方法对 77 个月度受孕队列的双胞胎次级性别比进行了计算，这些队列跨越 2013 年 8 月至 2019 年 12 月，以检测在大流行开始时处于妊娠晚期的异常受孕队列。
在三个受孕队列（即 2019 年 7 月、9 月和 10 月）中，双胞胎次级性别比低于预期值（均 p<0.05），这些队列在宫内暴露于大流行开始时。
我们的结果增加了先前与宫内选择一致的发现。宫内选择在塑造活产儿队列特征方面的作用，特别是在 COVID-19 大流行期间，值得进一步研究。
