Interpregnancy interval, which is the time between the end of one pregnancy and conception of the subsequent pregnancy, is a modifiable risk factor that has the potential to prevent a fraction of stillbirths—particularly in low-income and middle-income countries (LMICs) where 98% of global stillbirths occur. Most of these stillbirths are attributable to poor maternal health and inadequate antenatal and intrapartum care. Several studies have reported associations between stillbirth and interpregnancy interval.^,  Whether these associations reflect a causal relationship remains open for discussion, despite the existence of plausible biological pathways. Interpregnancy interval per se cannot be randomly assigned to women directly, so cannot be studied in the gold standard format of a randomised controlled trial. We usually rely on well-designed observational studies to control for confounding of associations with the exposure, which is time. Although the intrinsic temporal nature of the exposure requires careful consideration of bias, it also offers opportunities for causal inference.

中文翻译：

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对低收入和中等收入国家孕期间隔导致死产的假设提出了挑战。

怀孕间隔是指一次怀孕结束至以后再怀孕之间的时间，是一种可改变的危险因素，有可能预防死产的发生，特别是在低收入和中等收入国家（LMIC） 98％的全球死产发生。这些死产大多数是由于孕产妇健康状况不佳以及产前和产时护理不足所致。几项研究报告了死产与妊娠间隔之间的关联。^， 尽管存在合理的生物学途径，但这些关联是否反映因果关系仍有待讨论。妊娠间隔本身不能直接随机分配给女性，因此不能以随机对照试验的黄金标准格式进行研究。我们通常依靠精心设计的观察性研究来控制与暴露（时间就是时间）之间的混淆。尽管曝光的内在时间性质需要仔细考虑偏差，但它也提供了因果推断的机会。