Long answer: While there is no "safe" dose of radiation to a developing fetus, dose to a developing fetus is likely very, very low if done with modern mammography equipment. Most mammogram units have a plate that is installed perpendicular to the machine just below the imaging plate. This ensures that a woman’s stomach does not get in the way of the image (if she is overweight). This plate is also shielded to avoid excess radiation dose to a woman’s stomach/bowels. In your wife’s case, this likely provided shielding for the developing fetus in her uterus. Although the risk to the fetus was diminishingly low, I would still talk with her OB-GYN about your concerns.