How long should a parent be concerned about jaundice with their newborn?

Depends on why: Transitional jaundice is seen in as many as 1/3 of newborns. In most it disappears as their system adapts to the new work of out of womb living usually in a week. If it is intense, caused by additional issues of blood breakdown, illness, liver disease it can remain an issue. I've had 1 go to liver transplant & many need prolonged care. Though minor for most it can be a real issue.