This appears to be the most critical time when abnormal features can be caused. Alcohol may affect the way cells grow and arrange themselves as they multiply, altering tissue growth in the part o f the fetus that is developing at the time of exposure. The brain is particularly sensitive to alcohol which diminishes the number of cells growing in the brain. Consequently, the brain is smaller and often its neurons are found in the wrong places. The early loss of cells in the developing fetus may help explain overall retarded growth and low birth weight in babies with FAS.
In the second Trimester:-
Miscarriage is a major risk during this time. There may be times of fetal distress related to binge drinking (irregular periods of heavy drinking).
In the third trimester:-
During this period the fetus normally undergoes rapid and substantial growth. Alcohol can impair this growth. This is also the time of greatest brain development. Research with animals indicates the brain and central nervous system are at great risk during the third trimester