Department of Obstetrics and Gynaecology, Faculty of Medicine, University of British Columbia, Vancouver, Canada.
Department of Epidemiology, Biostatistics, and Occupational Health, Faculty of Medicine, McGill University, Montreal, Canada.
Am J Epidemiol. 2019 Jan 1;188(1):17-21. doi: 10.1093/aje/kwy195.
Numerous observational studies have shown that infants born after short interpregnancy intervals (the interval between birth and subsequent conception) are more likely to experience adverse perinatal outcomes than infants born following longer intervals. Yet it remains controversial whether the link between short interpregnancy interval and adverse outcomes is causal or is confounded by factors such as low socioeconomic position, inadequate access to health care, and unintended pregnancy. Sibling comparison studies, which use a woman as her own control by comparing exposure and outcome status of her different pregnancies (i.e., comparing sibling offspring), have gained popularity as a strategy to reduce confounding by these difficult-to-measure factors that are nevertheless relatively stable within women. A variant of this approach, used by Regan et al. (Am J Epidemiol. 2019;188(1):9-16) and reported in this issue of the Journal, is a maternally matched design based on a single interpregnancy interval per woman. Using real and simulated data, we highlight underappreciated shortcomings of these designs that could limit the validity of study findings. In particular, we illustrate how the single-interval variant appears to derive estimates from comparisons between different mothers, not within mothers. Future studies of optimal birth spacing using sibling comparison designs should examine in detail the potential consequences of these methodological limitations.
大量观察性研究表明，与间隔较长的妊娠相比，间隔较短的妊娠（分娩与后续受孕之间的间隔）所生婴儿更有可能出现不良围产期结局。然而，短间隔妊娠与不良结局之间的联系是因果关系，还是受到诸如社会经济地位低、获得医疗保健机会不足和意外怀孕等因素的混杂，仍存在争议。同胞比较研究通过比较女性不同妊娠的暴露和结局状况（即比较同胞后代），以女性自身为对照，作为一种减少这些难以衡量的因素混杂的策略而受到欢迎，尽管这些因素在女性内部相对稳定。这种方法的一个变体，由 Regan 等人使用（Am J Epidemiol. 2019;188(1):9-16）并在本期杂志上报道，是一种基于每个女性单次妊娠间隔的母体匹配设计。我们使用真实和模拟数据，强调了这些设计中未被充分认识到的缺陷，这些缺陷可能会限制研究结果的有效性。特别是，我们说明了单间隔变体如何似乎是从不同母亲之间的比较中得出估计值，而不是从母亲内部得出。未来使用同胞比较设计研究最佳生育间隔的研究应详细研究这些方法学限制的潜在后果。
