Fig. 4

Adjusted odds ratio (with 95% confidence interval in parenthesis) for the prevalence of preterm birth by each demographic region identified on a map of California for the period 2007–2016. Northern and Sierra region is the reference group
Adjusted odds ratio (with 95% confidence interval in parenthesis) for the prevalence of preterm birth by each demographic region identified on a map of California for the period 2007–2016. Northern and Sierra region is the reference group