Maternal age and incidence of low birth weight at term: a population study.

A total of 184,567 singleton live births with gestational ages of 40 weeks were examined from the 1980-1984 Illinois birth certificate data to determine the independent effect of maternal age on the incidence of low birth weight at term. The incidence is highest in mothers less than 17 years of age (3.2%) and gradually declines with advancing maternal age to reach 1.3% in women aged 25 to 34 years. It increases to 1.7% for those greater than 35 years of age. To separate out the independent effect of maternal age on the incidence of low birth weight infants at term, the presence of other maternal factors, such as race, education, parity, marital status, and prenatal care, were adjusted by use of a series of multiple logistic regression analyses. All of these analyses consistently demonstrated that the adjusted risk for low birth weight at term is the lowest in teenagers and increases with advancing maternal age. These results indicate that the high incidence of this factor in young mothers apparently reflects their poor sociodemographic and prenatal care status. Advancing maternal age is associated with a decreased potential for fetal growth, possibly reflecting biologic aging of maternal tissues and systems or the cumulative effects of disease.