|Acute Radiation Dose∗to the Embryo/Fetus||Time 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||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|
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).