Medical conditions which might hinder healing, such as haemopholia or connective tissue disorders, will require special treatment. Whether circumcision is carried out or not will be a matter for parental discretion, but if the boy is circumcised special procedures will need to be in place. Premature or jaundiced babies will need to wait until they are fully healthy before circumcision.
The list of medical contra-indications may look worrying, but most of these conditions are rare. The most common, hypospadias, occurs in about 1 in 1,000 boys and is easily repaired. The repair will normally involve circumcision, so your boy will still end up circumcised. Our "best guess" is that clinical contra-indications to infant circumcision occur in no more than 2% of live male births, ans most merely require delaying the operation until the problem is fixed.
Website of Stanford School of Medicine.