Joke:  It must be Milwaukee, Pat.  When  I lived there, I always got yeast infections with antibiotics.   Once I came to California (thirty years ago), I never had a yeast infection again.  Well, not quite true.  I did have some yeast infections, but they were not colateral with courses of antibiotics. 

In answer to your post, no, it is not necessarily true that mom received an antibiotic, just because she had an IV.  Many of our moms do not get anti-biotics, few of our moms don't get IV's.

Indications for IVs, other than antibiotics:

        Administration of Magnesium Sulfate for either pre-term labor   (PTL), or for pre-eclampsia;  

        IV hydration, either for suspected pre-term labor or for        hyperemesis or other problems;

        Pitocin induction;

        History of hemmorhage with previous labor or delivery;

        Previous C/S;

        Administration of some pain medications, and concommitant with  all epidurals, spinals, etc.;

        Grandmultiparity;

        Excessive blood loss with this labor and/or delivery; abruption,        etc.

        Maternal exhaustion with this labor (prolonged labor);
and probably others I can't immediately think of.

Indications for antibiotics:

        Prolonged rupture of membranes may require a prophylactic dose of atbx depending on hospital protocol;

        Pre-term ROM, again, as above;

        Beta strep carriers;

        C/S or sometimes manual removal of placenta or uterine exploration usually get a one-time dose of atbx prophylactically;

        Moms with MVP or other heart problems may get prophylactic atbx at 8 cm or at delivery.

Then after delivery, antibiotics seem only to be the case if moms have infections.

Again, these are off the top of my head, the usual things I see as an RN an antipartum, L&D, and post-partum.

Chanita, San Francisco