Temporal trends, patterns, and predictors of preterm birth in California from 2007 to 2016, based on the obstetric estimate of gestational age.

Overall, there were highly significant ( p < .001) differences in the prevalence of PTB, compared with the reference groups, for each maternal sociodemographic characteristic and perinatal health behavior studied: maternal age, race and ethnicity, education level, nativity, demographic region, smoking status, prepregnancy BMI, source of prenatal health care insurance payment, use of first-trimester prenatal care, and parity (Table 2 ).

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