Unless you KNOW that he's making a lot of money, I wouldn't assume it at all. Malpractice rates for OB's are sky-high in many states, and with the expenses of running an office and paying off med school loans (usually for 20 years) there are many that are not doing all that well. I know that in my state (PA) several offices have closed down recently because of this. That said, maybe a gift certificate to a nice restaurant? Or, if you want to get something personalized, maybe an engraved picture frame from a place like Things Remembered.