We are trying to have another child what are the chance of it having a birth defect?

Ok I know this is just normal people but maybe someone here has had t he same experience. We are trying to get pregnant again but we are a little worried, my youngest son was born with a bilateral cleft palate and lip and i was just curious what that chance of another having the same problem? We have another child with no problems and no one in our family have had this and wedidn'tt know about this until he was born so it was a surprise at the least and when i do get pregnant can i make the dr check for this on new baby so if so we will be prepared this time?