For the purpose of stratifying the level of prenatal exposure for the SPM analyses, the median number of drinks for those who reported any drinking during pregnancy was first determined. Those mothers who reported no drinking or drinking less than the median for the sample were classified as no or low exposure mothers and those with drinking above the median as high exposure. Accordingly, offspring who had prenatal exposure equal to or greater than 54 drinks during the pregnancy were categorized as prenatally exposed and those with mothers reporting less than 53 drinks were considered to be prenatally low or unexposed. To provide a more refined estimate of prenatal effects on offspring, comparisons were made between those grouped by whether the mother did not drink during pregnancy (nonexposed) versus those who drank less than the median (low-exposure), and again using the nonexposed versus those with mothers having greater than the median use (high-exposure).
