1. Nutrition : Severe protein malnutrition results in
twice the number of defects.
Fewer brain cells are produced, and
learning ability may be permanently affect
2. Excessive amounts of vitamins : Vitamin D is essential,
but excessive amounts may result in a form of mental retardation.
Too much vitamin A and K may also be harmful
3. Drugs : Many drugs affect the development of the fetus.
Even aspirin has been shown to inhibit growth of human fetal cells
(especially kidney cells) cultured in the laboratory.