Advanced parental age is an independent risk factor for term low birth weight and macrosomia.

We aimed to investigate association between parental age and the risks of term low birth weight and macrosomia. This was a retrospective cohort study using a national database including 2,245,785 term singleton live births with complete parental age data. Old parental age was defined as 35 years or older. Odd ratios (OR) for term low birth weight and macrosomia were analyzed using univariate and multivariate logistic regression analysis. Neonatal sex, maternal occupation, parity, nationality, age, and paternal age were significant factors of term low birth weight and macrosomia, in univariate analysis. In multivariate analysis, old maternal age (≥35 years old) showed increased odds of term low birth weight and macrosomia (aOR = 1.122, 95% CI: 1.083 -1.162; and aOR = 1.166, 95% CI: 1.143 - 1.189, respectively). Similarly, old paternal age (≥35 years old) showed increased odds of term low birth weight and macrosomia (aOR = 1.090, 95% CI: 1.058 -1.122; and aOR = 1.101, 95% CI: 1.083 - 1.119, respectively). Maternal education that lasted more than 12 years had reduced odds of term low birth weight and macrosomia (OR = 0.817, 95% CI: 0.792 -0.842; and OR = 0.894, 95% CI: 0.879 - 0.91, respectively). Paternal education that lasted more than 12 years also had reduced odds of term low birth weight and macrosomia (OR = 0.865, 95% CI: 0.84 -0.892; and OR = 0.897, 95% CI: 0.881 - 0.913, respectively). This study suggests that not only maternal age but also paternal age are significantly associated with term low birth weight and macrosomia. In addition, parental education levels are also associated with term low birth weight and macrosomia.