NCI is conducting a study to evaluate potential adverse reproductive outcomes associated with prenatal exposure to Iodine-131 as a result of radioactive releases from the nuclear accident at the Chernobyl power plant. The target population is a well-defined cohort of 2,582 mother-child pairs from three contaminated areas of northern Ukraine characterized by mild-moderate iodine deficiency. The principal objective of the analyses will be to examine the relationship of individual thyroid iodine 131 (I-131) dose and each of the specified reproductive outcomes. A secondary aim will be to evaluate the independent and joint effects of maternal iodine deficiency on study endpoints.