Montana subscriber
Answer: You can perform any service that would not normally be part of the global package in the sense that you can report it separately - unless the ob-gyn performs an ultrasound.
The ob-gyn can prescribe vitamins and order labs because these minor activities do not impact the level of E/M service.
However, carriers might find coding a GynProbe more questionable, because the ob-gyn would not have ordered this service unless the patient was pregnant. Keep in mind that payers usually characterize the GynProbe as a separately billable service. Therefore, the payer may not care.
Just do not get caught doing counseling for the pregnancy and then taking credit for it by coding a higher level of E/M service.
Those kinds of things - an ultrasound or taking pregnancy measurements - will convince payers that the ob-gyn started the global care.