Brief report: Pregnant by age 15 years and substance use initiation among US adolescent girls.

We examined substance use onset and associations with pregnancy by age 15 years. Participants were girls ages 15 years or younger (weighted n = 8319) from the 1999-2003 Youth Risk Behavior Surveillance System (YRBS). Multivariable logistic regression examined pregnancy as a function of substance use onset (i.e., age 10 years or younger, 11-12, 13-14, and age 15 years) for alcohol, cigarettes and marijuana, controlling for race/ethnicity and metropolitan location. Of girls pregnant by age 15 years (3% of the sample, weighted n = 243), 16% had smoked marijuana by age 10 years and over 20% had smoked cigarettes and initiated alcohol use by age 10 years. In the multivariable analysis, marijuana use by age 14 years and/or cigarette smoking by age 12 years clearly distinguished girls who became pregnant by age 15 years and is perhaps due to a common underlying risk factor.