There are several breakdown products from aspartame that are major causes for concern and have caused countless toxicity reactions in the general public (see 160+ pages of samples on my web page). The concern of aspartame ingestion during pregnancy is not limited to obvious birth defects, but changes or damage to certain areas of the brain. The potential damage includes parts of the brain involved in complex learning as well as hormonal control (e.g., hypothalamus). Problems resulting from this sort of damage would not be seen until after the child reaches puberty. Neuroscientist, Dr. Russell Blaylock discusses this in some detail in his book, "Excitotoxins."