Effects of Environmental Chemical Exposure on Birth Defects (Except Cryptorchidism and Hypospadias)

Currently, the causes of birth defects remain unknown in approximately 80% of the cases. Here, the etiologies are likely multifactorial and may involve the genetic background, exposure to drugs, environmental chemical exposure, infections, maternal factors, and intrauterine mechanical factors. In this review, we discuss the effects of environmental chemical exposure on the incidence of birth defects by summarizing the previous epidemiological studies. Notably, chemical exposure was most frequently associated with elevated risks of central nervous system and congenital heart defects and oral clefts than with other types of birth defects. Although exposure to air pollutants, persistent organic pollutants, polycyclic aromatic hydrocarbons, and perfluorinated compounds were associated with increased risks, no substance-specific birth defects were identified. Many case–control studies had the limitation due to poor exposure assessment. In terms of the risk assessment, it is difficult that epidemiological study indicates the hazard identification including the dose-response relationship. We conclude that descriptions of the disease prevalence and individual chemical exposure levels are important roles of reproductive epidemiological study.