Curtin School of Population Health, Curtin University, Bentley, WA, Australia.
Curtin University, GPO Box U1987, Perth, WA, 6845, Australia.
Sci Rep. 2022 Nov 10;12(1):19214. doi: 10.1038/s41598-022-23719-3.
Restriction to analysis of births that survive past a specified gestational age (typically 20 weeks gestation) leads to biased exposure-outcome associations. This bias occurs when the cause of restriction (early pregnancy loss) is influenced by both the exposure and unmeasured factors that also affect the outcome. The aim of this study is to estimate the magnitude of bias resulting from left truncated data in the association between advanced maternal age and stillbirth. We simulated data for the causal pathway under a collider-stratification mechanism. Simulation parameters were based on an observed birth cohort from Western Australia and a range of plausible values for the prevalence of early pregnancy loss, unmeasured factor U and the odds ratios for the selection effects. Selection effects included the effects of maternal age on early pregnancy loss, U on early pregnancy loss, and U on stillbirth. We compared the simulation scenarios to the observed birth cohort that was truncated to pregnancies that survived beyond 20 gestational weeks. We found evidence of marginal downward bias, which was most prominent for women aged 40 + years. Overall, we conclude that the magnitude of bias due to left truncation is minimal in the association between advanced maternal age and stillbirth.
对超过特定胎龄（通常为 20 周妊娠）存活的分娩进行分析的限制会导致暴露-结局关联存在偏差。当限制的原因（早期妊娠丢失）受到暴露和未测量因素的影响，而这些因素也会影响结局时，就会出现这种偏差。本研究的目的是估计在母亲年龄较大与死产之间的关联中，由于左截断数据而导致的偏差程度。我们根据碰撞分层机制下的因果途径模拟了数据。模拟参数基于西澳大利亚州的一个观察性出生队列以及早期妊娠丢失、未测量因素 U 和选择效应的比值比的一系列合理值。选择效应包括母亲年龄对早期妊娠丢失的影响、U 对早期妊娠丢失的影响以及 U 对死产的影响。我们将模拟情景与在 20 孕周后存活的妊娠截断的观察性出生队列进行了比较。我们发现存在轻微的向下偏差的证据，对于年龄在 40 岁以上的女性最为明显。总的来说，我们得出结论，在母亲年龄较大与死产之间的关联中，由于左截断导致的偏差程度很小。
