Retin-A During Pregnancy & Skin Cancer Treatment: Risks and Alternatives

Question
Hi Dr Rappaport! In one of my pregnancy books it is stated that Retin-A should not be used during pregnancy because of harm to the fetus. On-line websites state the same but don't give a reason or harm. I was diagnosed with a BCC on my sternum that is being removed this Friday, and high risk damage on my lower lip for sun cancer. The dermotologist wants to do a Lip Reduction because the damage is so severe. However, she did opt to wait two months and prescribed Retin-A for me to apply nightly. She wants to see how deep the "cancer" has penetrated. Now, she is not aware I am pregnant(6wk). Do you know of any relation between Retin-A and pregnancy? How concerned should I be?(I have been using it nightly since April 9th on my lips)
Thank you for you time! I appreciate the clarity of your responses, you are a bonus to us!

Answer
Elevated serum concentrations of all-trans retinoic acid (Retin-A) in early gestation are considered teratogenic in humans. Because of its poor systemic absorption after topical administration, however, tretinoin is not thought to present a significant fetal risk. Congenital malformations have been reported followiing topical use of this compound and althoough a causal association has not been established, may reflect greater than normal fetal exosure from higher than usual maternal doses or enhanced systemic absorption ,or biased reporting of adverse outcomes. Most of the evidence however, indicates that topical tretinoin does not increase the risk for congenital malformations. It is considered a category C medication which can be used during pregnancy if the advantages outweigh the risks. In your case, I would mention to your dermatologist that you are pregnant and see if he wants you to continue the medication. HOwever, I doubt that you have done any harm so far.