It has been shown in studies that exposure to over 10 rads (the unit of measurement for absorbed radiation) has been shown to increase the risks for mental retardation and eye abnormalities in an unborn baby. For this reason it is important to know about any x-ray your doctor or dentist proposes and to discuss any risks with them.
The most important thing to consider in regard to x-rays and pregnancy is that there are different types of x-rays, each with differing amounts of radiation. In general, most diagnostic x-rays don’t expose your baby to more than 5 rads. Dental x-rays in particular will expose your baby to approximately 0.01 millirads. In other words, you would need to have 100,000 dental x-rays for your baby to receive 1 rad, and 1,000,000 dental x-rays to reach the dangerous level of 10 rads. To put int all into perspective, your baby will be exposed to about 100 millirads of natural radiation from the sun and the earth while you are pregnant.
When you have a dental x-ray, make sure the dentist or dental technician knows that you are pregnant so she can properly shield you. This will even further reduce the amount of radiation your baby is exposed to.