Separate Cox Regression survival analyses were conducted to assess the effects of prenatal exposure to alcohol or cigarettes on offspring SUD or smoking outcome using relevant covariates (SES, gender, and other prenatal exposures). In order to determine the relative contribution of risk and prenatal exposures to offspring substance use outcomes, survival analyses were conducted within the HR group in which offspring share a similar genetic loading for SUD but varying prenatal exposures. Given the collinearity between risk group status and substance use during pregnancy (i.e. lower rates and amounts of prenatal exposures among low-risk offspring), a statistical interactive design between risk and prenatal exposure could not be performed. Because offspring from multiplex, alcohol dependent families are at increased risk for both alcohol and drug use disorders (Hill et al., 2011), initial analyses assessed the broader category of offspring SUD. Significant relationships between prenatal exposures and SUD were subsequently assessed separately by alcohol and drug use disorders.
