Table 10

Estimates of Adverse Embryonic and Fetal Events as a Function of Fetal Radiation Dose

Acute Radiation Doseto the Embryo/FetusTime Post Conception
Blastogenesis (up to 2 wks)Organogenesis (2–7 wks)Fetogenesis
(8–15 wks)(16–25 wks)(26–38 wks)
< 0.05 Gy (5 rads)Noncancer health effects NOT detectable
0.05-0.50 Gy (5-50 rads)Incidence of failure to implant may increase slightly, but surviving embryos will probably have no significant (noncancer) health effects
  • Incidence of major malformations may increase slightly

  • Growth retardation possible

  • Growth retardation possible

  • Reduction in IQ possible (up to 15 points, depending on dose)

  • Incidence of severe mental retardation up to 20%. depending on dose

Noncancer health effects unlikely
> 0.50 Gy (50 rads)
The expectant mother may be experiencing acute radiation syndrome in this range, depending on her whole-body dose.
Incidence of failure to implant will likely be large. depending on dose, but surviving embryos will probably have no significant (noncancer) health effects
  • Incidence of miscarriage may increase, depending on dose

  • Substantial risk of major malformations such as neurological and motor deficiencies

  • Growth retardation likely

  • Incidence of miscarriage probably will increase, depending on dose

  • Growth retardation likely

  • Reduction in IQ possible (>15 points, depending on dose)

  • Incidence of severe mental retardation >20%, depending on dose

  • Incidence of major malformations will probably increase

  • Incidence of miscarriage may increase, depending on dose

  • Growth retardation possible, depending on dose

  • Reduction in IQ possible, depending on dose

  • Severe mental retardation possible, depending on dose

  • Incidence of major malformations may increase

  • Incidence of miscarriage and neonatal death will probably increase depending on dose§

Reproduced with permission from the Centers for Disease Control and Prevention (41).

Note: This table is intended only as a guide. The indicated doses and times post conception are approximations.

  • Acute dose: dose delivered in a short time (usually minutes). Fractionated or chronic doses: doses delivered over time. For fractionated or chronic doses the health effects to the fetus may differ from what is depicted here.

  • Both the gray (Gy) and the rad are units of absorbed dose and reflect the amount of energy deposited into a mass of tissue (1 Gy = 100 rads). In this document, the absorbed dose is that dose received by the entire fetus (whole-body fetal dose). The referenced absorbed dose levels in this document are assumed to be from beta, gamma, or x-radiation. Neutron or proton radiation produces many of the health effects described herein at lower absorbed dose levels.

  • A fetal dose of 1 Gy (100 rads) will likely kill 50% of the embryos. The dose necessary to kill 100% of human embryos or fetuses before 18 weeks' gestation is about 5 Gy (500 rads).

  • § For adults, the LD50/60 (the dose necessary to kill 50% of the exposed population in 60 days) is about 3-5 Gy (300-500 rads) and the LD100 (the dose necessary to kill 100% of the exposed population) is around 10 Gy (1000 rads).