Survey Research Center, University of Michigan Institute for Social Research, Ann Arbor, Michigan, USA
Urban Indian Health Institute, Seattle, Washington, USA.
BMJ Open. 2020 Feb 5;10(2):e032476. doi: 10.1136/bmjopen-2019-032476.
Preterm births (PTBs) represent significant health risks, and several studies have found associations between high outdoor temperatures and PTB. We estimated both the total and natural direct effects (independent of particulate matter, ozone and nitrogen dioxide air pollutants) of the prior 2-day mean apparent temperature (AT) on PTB. We evaluated effect modification by maternal age, race, education, smoking status and prenatal care.
We obtained birth records and meteorological data for the Detroit, Michigan, USA area, for the warm months (May to September), 1991 to 2001. We used a time series Poisson regression with splines of AT, wind speed, solar radiation and citywide average precipitation to estimate total effects. To accommodate multiple mediators and exposure-mediator interactions, AT inverse odds weights, predicted by meteorological and air pollutant covariates, were added in a subsequent model to estimate direct effects.
At 24.9°C relative to 18.6°C, 10.6% (95% CI: 3.8% to 17.2%) of PTBs were attributable to the total effects of AT, and 10.4% (95% CI: 2.2% to 17.5%) to direct effects. Relative excess risks of interaction indicated that the risk of PTB with increasing temperature above 18.6°C was significantly lower among black mothers and higher among mothers less than 19, older than 30, with late or no prenatal care and who smoked.
This additional evidence of a direct association between high temperature and PTB may motivate public health interventions to reduce extreme heat exposures among pregnant women, particularly among those who may have enhanced vulnerability.
早产（PTB）代表着重大的健康风险，有几项研究发现，室外高温与 PTB 之间存在关联。我们估计了前 2 天平均表观温度（AT）对 PTB 的总效应和自然直接效应（独立于颗粒物、臭氧和二氧化氮空气污染物）。我们评估了母体年龄、种族、教育、吸烟状况和产前保健的效应修饰作用。
我们获得了美国密歇根州底特律地区的出生记录和气象数据，时间为 1991 年至 2001 年的温暖月份（5 月至 9 月）。我们使用时间序列泊松回归，用 AT、风速、太阳辐射和全市平均降水量的样条进行拟合，以估计总效应。为了适应多个中介和暴露-中介相互作用，我们在后续模型中添加了通过气象和空气污染物协变量预测的 AT 逆优势权重，以估计直接效应。
与 18.6°C 相比，24.9°C 时，归因于 AT 总效应的 PTB 发生率为 10.6%（95%CI：3.8%至 17.2%），归因于直接效应的发生率为 10.4%（95%CI：2.2%至 17.5%）。交互的相对超额风险表明，对于高温超过 18.6°C，黑人母亲的 PTB 风险显著降低，而年龄小于 19 岁、大于 30 岁、产前保健较晚或没有、吸烟的母亲的 PTB 风险较高。
这进一步证明了高温与 PTB 之间存在直接关联，这可能促使公共卫生干预措施减少孕妇暴露于极端高温，特别是对于那些可能具有增强脆弱性的孕妇。
