A case-control study of maternal risk factors for thyroid cancer in young women (California, United States).

A population-based case-control interview study investigated whether reproductive factors are related to the striking female-over-male excess of thyroid cancer among women of reproductive age in Los Angeles County, CA (United States). As a separate component of that study, mothers of 153 cases and 140 controls who were age 40 or younger at diagnosis or reference date were interviewed by telephone to determine the significance of family and maternal risk factors in the subsequent development of thyroid cancer among the daughters. More case than control mothers experienced miscarriage prior to the index pregnancy (odds ratio [OR] = 2.0, 95 percent confidence interval [CI] = 1.1-3.5). Increased risk was associated with family history of thyroid cancer or other thyroid disease (OR = 2.1, CI = 1.2-3.6). More control than case mothers smoked during the index pregnancy (OR = 0.6, CI = 0.4-1.0); however, among mothers who smoked, case mothers smoked more. Case mothers experienced a greater increase in weight from minimum adult weight to weight at index pregnancy (P for trend = 0.01). Reports from mothers also confirmed the risk associated with the daughter's exposure to ionizing radiation from birth through adolescence; ionizing radiation remains the best-established risk factor for thyroid cancer.