Figure 4.

The relationship between the average temperature exposed during the whole pregnancy and the preterm birth risk in China Labor and Delivery Survey ($n=\mathrm{70,818}$). (See Tables S9 for corresponding numeric data.) Note: Cox proportional hazard regression incorporated with penalized cubic spline was used to examine exposure-response associations. HRs represent a 1-unit increase in extreme weather events and are presented with a 95% CI. All models were adjusted for maternal age, maternal ethnicity, maternal education, insurance type, child sex, parity, GDP per capita, geographic region, conception season, conception year, ${\mathrm{PM}}_{2.5}$, and ${\mathrm{O}}_3$. CI, confidence interval; GDO, gross domestic product; HR, hazard ratio; ${\mathrm{PM}}_{2.5}$, particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$.