1. The document describes fetal development from pre-embryonic to embryonic stages, covering organogenesis and development of major organs from 4-12 weeks.
2. It then covers types of birth defects such as malformations, disruptions, deformations, and dysplasias which can be caused by genetic or environmental factors such as infections, drugs, or radiation exposure during pregnancy.
3. The major causes of birth defects are described as genetic factors in 40-60% of cases, maternal illnesses and infections in 20-25% of cases, and multifactorial and unknown causes in 12-25% and 10-13% of cases respectively.