My 2child had polydactyly she had 12finger and toes now im20weeks pregnant with my 3child what are the chances of congential defects in baby.plz help!

Higher than usual: Obviously you've had several children with a rare, congenital condition. Granted it's not that rare, but it's rare enough that having two children with the same issue signifies there may be something in your genetic code to make this more likely. An extra finger or toe can be dealt with as you know, so if it happens, schedule an appointment with a good plastic surgeon.