What is considered the least radiation dose to the fetus that could cause spontaneous abortion?

The least radiation dose to the fetus that could potentially cause spontaneous abortion is generally considered to be around 50 rads. This threshold is based on various studies that have assessed the effects of radiation exposure on pregnancy outcomes. While lower doses may also pose some risk, the consensus in the field of radiation safety and fetal development indicates that around 50 rads represents a significant level where adverse effects, including spontaneous abortion, become increasingly probable.

It's essential to recognize that the risk is cumulative and can depend on various factors, including the timing of exposure during gestation and individual susceptibility. Higher doses further increase the likelihood of adverse effects, which is also reflected in the answer that indicates greater doses above this level contribute to more severe outcomes. Understanding this threshold is crucial for those working in radiography and related fields when managing radiological safety, especially regarding pregnant patients.