This is not talking about giving antibiotics during c-section or after. This new guideline is talking about giving antibiotics within the hour before delivery. Before most of the c-section Mama's probably did have antibiotics but now c-section Mama's will get them before delivery. Just wanted to point that out.
FYI for those with allergies: if your known drug allergies are listed you will not necessarily be asked about individual antibiotics; I work in SICU and docs regularly skim the list of allergies and choose antibiotics based on cross-allergy. The patients/families aren't informed. Only once have I seen docs ask a patient about specific antibiotics because the list of allergies took up many pages, and even then my guess is they were only asking her because she had had an episode of anaphylaxis during that hospital stay. If it had been a prior admission she'd have been given whatever they wanted to try and observed for a reaction.
If you're allergic to penicillin or macrolides or something common like that, you're getting a stronger one like vancomycin. The point is if you don't want a specific drug during surgery you need to be very, very specific in the consents you sign, but will probably still be given antibiotics even if you specifically refuse.