While research on early childbearing has largely focused on women, we include men as well as women by examining age at first childbirth rather than age at first pregnancy. To ensure specificity of observed AD effects, we select as control variables a host of well-documented correlates of AD and reproductive timing, including sociodemographic characteristics, history of psychopathology, and family and childhood risks. History of regular smoking is also included as regular smoking increases risk for AD (Grucza & Beirut, 2006; Madden, Bucholz, Martin, & Heath, 2000) and smoking has been linked with infertility and spontaneous abortion in women who smoke (Augood, Duckitt, & Templeton, 1998; DHHS, 2004) and with lower sperm count and motility in men (Vine, 1996). Smoking is also associated with poor overall physical health (DHHS, 2004).
