Department of Epidemiology and Biostatistics, College of Human Medicine, Michigan State University, East Lansing, Michigan.
Centers for Epidemiology and Environmental Health, School of Public Health, Brown University, Providence, Rhode Island.
Paediatr Perinat Epidemiol. 2019 Mar;33(2):154-161. doi: 10.1111/ppe.12534. Epub 2019 Jan 24.
Making causal inference regarding impacts of macrolevel economic conditions during pregnancy on pregnancy outcomes is hampered by the presence of unmeasured variables that may influence women's probability of giving birth under certain economic conditions (ie, exposure) as well as her pregnancy outcomes. Maternal fixed-effects (FE) analyses, in which the association between exposure and outcomes is estimated within mothers who had discordant outcomes, can control for such unmeasured variables when they are invariant across pregnancies.
We utilised a maternally linked data set of all singleton births in Michigan from 1990 to 2012 (n = 2 657 272 for full sample; n = 269 943 for FE analytic sample) to examine the relationship between state-level unemployment rates during pregnancy and preterm birth (PTB, <37 weeks' gestation). Measured maternal characteristics that change across pregnancies, for example, age, marital status, education, parity, and infant sex, were included as covariates in the model.
Using an FE approach, we found that each one percentage point increase in state unemployment in the first trimester of pregnancy was associated with a modest 3% increase in odds of PTB. Our results were consistent with previously published results in a national sample and held across random- versus fixed-effect models, analytic samples, and outcome measures.
Our findings provide further evidence that economic downturn during early pregnancy may be associated with modest increases in PTB.
在怀孕期间，宏观经济状况对妊娠结局的影响进行因果推断，受到未被测量的变量的阻碍，这些变量可能会影响女性在特定经济状况下（即暴露）生育的可能性以及她的妊娠结局。当未被测量的变量在整个孕期保持不变时，母体固定效应（FE）分析可以控制这些变量。
我们利用了密歇根州从 1990 年到 2012 年的母婴关联数据，对所有单胎分娩（全样本 2657272 例；FE 分析样本 269943 例）进行了分析，以检验妊娠期间州级失业率与早产（PTB，<37 周妊娠）之间的关系。模型中包括了在整个孕期发生变化的可测量的母体特征，例如年龄、婚姻状况、教育程度、产次和婴儿性别等作为协变量。
使用 FE 方法，我们发现妊娠早期每增加一个百分点的州失业率，PTB 的几率就会增加约 3%。我们的结果与全国样本中之前发表的结果一致，且在随机效应与固定效应模型、分析样本和结局测量方面都一致。
我们的发现进一步证明，妊娠早期的经济下滑可能与 PTB 的适度增加有关。
