The most common source of radiation is diagnostic medical and dental x-rays. Monitoring is important where workers may be exposed to radiation on the job. Cats- yes, cats. Cats carry a parasite called Toxoplasma, which can be transmitted through their feces to pregnant women. In a small percent of pregnancies, Toxoplasma can infect the mother's placenta and the baby, resulting in birth defects, including mental retardation and blindness.
German measles is one of few viruses that can cause serious birth defects.
Prevention is achieved through the increased use of the rubella vaccine. Use during pregnancy may produce premature birth, low birth weight, and poor mental development. Avoiding tobacco and alcohol use is important and sometimes taken too much for granted. Down syndrome is one of the most common chromosome defects. It occurs more often in pregnancies among older women, but it can occur in any pregnancy for no apparent reason.