Table 7

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

Acute Radiation Dose to 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 (35).

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 to 5 Gy (300 to 500 rads) and the LD100 (the dose necessary to kill 100% of the exposed population) is around 10 Gy (1,000 rads).