Maternal smoking and irradiation during pregnancy as risk factors for child leukemia.

The effect of joint exposure to diagnostic X-rays and maternal smoking during pregnancy was compared in a case-control study of 216 children with cancer (128 cases with acute lymphoblastic leukemia [ALL] and 88 with solid tumors) and 301 control children with insulin-dependent diabetes mellitus (IDDM). Exposure to diagnostic X-rays combined with smoking of ten or more cigarettes per day gave a relative risk of 3.6 (95% CI, 1.8 to 7.0) and a positive dose response relation for ALL in the offspring (p less than 0.001). When examined alone, X-rays gave a relative risk of 1.8 (95% CI, 1.1 to 3.1), and smoking a relative risk of 2.2 (95% CI, 1.1 to 4.5). No similar trend was seen for solid tumors. Potential confounding was examined after stratification on maternal smoking-diagnostic X-ray exposure and each of potential confounders, but there was little change in the risk ratio. We conclude that the risk of ALL in the offspring was more than threefold higher when smoking was combined with diagnostic X-ray during pregnancy.