I personally had an experience with this last season. My female, Athena, caught an RI a week after ovulating. We ultrasounded her to verify conception, which was indeed verified. We chose Zosyn, which we believed to be the safest medicine for her. She had a normal pregnancy, and delivered the typical 115 days POS.
She delivered 21 babies, 2 slugs. 10 of the 21 babies were still born, 1 baby was euthanized the next day by my vet due to an umbilicus that was over 1/2 inch wide. Of the 10 remaining alive, there were underbites, kinks, domed heads, etc. only a few of the snakes began eating on their own, and I began forcefeeding a few. In hindsight, I would have euthanized the whole litter. That said, 6 babies are still alive, and doing well in pet only homes. The other 4 failed to thrive, and eventually passed. If at all possible, avoid antibiotics during gestation - we just don't know enough about how they'll affect our lady snakes and their babies. If desired, I can post pictures of the defects
i've now gotten some mixed reviews. some experienced things like yours and others had no problems at all. One person I know used Tylan sucessfully but