Pregnancy Risk with Sulfa & Birth Control: A Medical Perspective

Question
I am a 22y/o mostly healthy female.I have been taking othro-tri-cyclen-lo as prescribed for a couple of years, my last cycle was Thursday Sept 22nd-Sept. 25th. I was admitted to the ER for a kidney stone on Thursday Sept 29th, put on Bactrim DS for 5 days-Tk 1 t po BID.I was sexually active on Thursday Oct 6th. I did use a Vaginal Contraceptive Film(VCF) and have continued taking my BCP, what is the likely hood of me becoming pregnant? Thank you for your help.

Answer
It is unlikely that you would become pregnant if you had not stopped the pills. Bactrim does not lower the efficacy of birth control pills, especially since you were also using contraceptive foam. If your last period started on September 29, the earliest you could have ovulated (if you were not on the pill) would be October 12. Even if you were not using any protection, it is too early in the cycle to conceive. Don't worry.