[Pregnancy and medical irradiation; summary and conclusions from the International Commission on Radiological Protection, Publication 84].

Prenatal exposure to ionising radiation as used during most diagnostic procedures generally presents no increased risk of prenatal death, malformation or impairment of mental development (i.e. deterministic effects) compared to the background incidence of these entities. Higher doses of radiation used in therapeutic procedures can result in significant foetal harm. In general, malformations only occur above a threshold dose of 100-200 mGy. These doses are not normally reached with most properly executed diagnostic procedures. During the period from 8 to 25 weeks after conception, the central nervous system is particularly sensitive to radiation. Foetal doses in excess of about 100 mGy may result in a decrease in IQ. Between 8-15 weeks after conception, a foetal dose of 1000 mGy (1 Gy) reduces IQ by about 30 points. This reduction is less marked during the period from 16-25 weeks. At foetal doses of 1000 mGy in the period from 8 to 15 weeks after conception the risk of severe mental retardation is about 40%. During the period from 16 to 25 weeks, this risk is practically zero at a dose of 1000 mGy. Radiation exposure of the embryo/foetus is associated with an increased risk of tumour induction (stochastic effect). Recent absolute risk estimates for fatal cancer risk for ages 0-15 year after in utero irradiation have been estimated to be 6% per Gy (0.06% per 10 mGy). For the whole life span this risk is about 15% per Gy (0.15% per 10 mGy). Pre-conception irradiation of either parent's gonads has not been shown to result in increased cancer or malformations in the children.