Will there be any advserse effect on my baby if i used retin a (tretinoin) 0.5mg for about the first 6 weeks of pregnancy on my face alone?

YES!: In the beginning the embryo consists of just one cell which divides into two cells, they into 4, then 8 etc. Early on any damage to a cell will have catastrophic results because if is one of the first 4 cells then 1/4 of the whole body would not develop. Damage done this early brings about a miscarriage. Later on when the baby has all its parts then damage to a cell leads to defects in that part.

No: It should probably be avoided once you found out you're pregnant, just to be safe. However oral forms of iso-tretenoin are very dangerous to your fetus and should be avoided.

Doubt it: We know oral preparations of this drug can have negative effects, which gives us caution. However, the skin preparations are a class C drug in pregnancy. This means they have no controlled studies on the issue to give it a better rating. Since skin application does not lead to a significant blood level, it is unlikely to cause problems.