Multinomial logistic regression models were used to estimate
the association between both paternal and maternal
prenatal depression and very and moderately preterm birth.
Model 1 was adjusted for calendar year of birth and maternal
age as a continuous variable, with quadratic terms of
maternal age, parity, paternal education, and paternal age
(45 years). In model 2 we further adjusted for
maternal smoking, BMI category, and chronological order
of parental depression.