"The consequence of radiation exposure in fetuses is mostly based on observations rather than based on scientific research. Ethical issues prohibit researching on the fetus. Therefore, most of the data on the impact of radiation on the fetus derives from observations of patients who suffered Japan’s Hiroshima bombing and the Chernobyl nuclear power plant disaster. Based on the observations made from the victims of the high level of radiation exposure, the consequences of radiation exposure can categorize into four broad groups, including pregnancy loss, malformation, developmental delay or retardation, and carcinogenesis. Pregnancy loss most often happens when radiation exposure happens during early gestation (less than two weeks)."