Thanks for the query.
Resorcinol comes under category C drugs in pregnancy
according to FDA.
So there may be some risk to the fetus.
Though there are no more well controlled studies, better to be on safe side.
You can use creams that contain alovera, vitamin E
Which are natural products and also help in preventing the excessive melanin
You have to start the cream before starting the marks itself.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429