Which of the following is approx. the least radiation absorbed dose to the fetus that could cause spontaneous abortion?

• A. 10 rads
• B. 25 rads
• C. 50 rads
• D. 100 rads

Answer: (C)

The main idea is that fetal radiation effects are dose-dependent, with a threshold for certain deterministic outcomes like miscarriage. When the fetal dose reaches around half a gray, there is a noticeable risk that abortion could occur; doses well below this threshold are unlikely to cause this outcome, while higher doses increase the risk further. In diagnostic practice, actual fetal doses are typically much lower than this threshold, so spontaneous abortion from standard imaging is uncommon. Thus, the approximate threshold around 0.5 Gy represents the smallest dose at which miscarriage becomes plausibly possible, explaining why that level is the correct reference point.