To the Editor.
—In their study of delayed childbearing and risk of poor perinatal outcomes, Cnattingius et al1 find an association between risks for the fetus and increasing maternal age. One variable they did not mention or control for is paternal age. I suspect a strong positive relationship exists between maternal and paternal age. Without at least including that variable, we have no way of knowing which is the stronger influence. I realize that such data, like cohabitation with the infant's father, smoking, or education, may be more difficult to obtain, but the issues warrant consideration.