While routine pre-operative & admission services are indeed included in the global surgical package, your code combination indicates to me that your doc was not the normal OB doc. Was your doc called in for a consult, recommended surgical intervention instead of a vaginal birth, and then asked to do the cesarean by the patient's normal OB doc? If so, I think you can make a case for payment of the 99252. I agree with the 57 modifier if this is the case, and maybe you just need to argue with the insurance carrier's determination by submitting documentation and pointing out that your doc provided a CONSULT and not routine hosp admission. You may not win, but I'd argue it just because that's how I roll... ;-)
If your doc was indeed the normal OB doctor of record, then nevermind, and I agree with preserene.
Becky, CPC