Pregnant?

[http://users.livejournal.com/--fourinchesx/]

History:
I'm on Gildess/Microgestrin, as a side note. About three weeks ago, I thought I had a YI, so I decided to go to the doctor. She did a swab for any other infections, but said it looked like a YI and prescribed the YI pill-thing. That was a Friday. That next Monday I got a call about my swab results and they said I had BV, which is whatever, and that they prescribed me Flagyl. I filled the prescription and went about my business. No sex for a week, due to the antibiotic, and everything was feeling better after the seven days.

Fast forward:
I had sex after being off the antibiotics, but only waited two days, which as I now know isn't long enough to wait after taking antibiotics on your BC. The end of my pack fell on June 6th (of the 28 day pack), which was this past Monday, and I was supposed to start my period on the 8th/9th. It didn't come. I waited until Saturday, just to be sure it wasn't going to spring up on me a little late, and it never came. I took a pregnancy test and it was negative. I guess my questions are:

1. Was it too early to take a pregnancy test and expect accurate results?
2. Could the antibiotic have affected my cycle?
3. How long are you really supposed to wait to have sex after being on antibiotics with BC?

I'm just freaking out, I'm hoping. :(

Comments

[gryphonwing.livejournal.com]

Metronidazole (Flagyl) is one of the antibiotics that has been shown to reduce the effectiveness of HBC, but not to the extent of rifampin. I was hoping I'd find a different answer for you when I searched... http://www.drugstore.com/ask/do-antibiotics-interact-with-birth-control-pills/qxa1091

I'm not sure of your timeline. Was the first Friday you mention the 20th of May? So you started your antibiotics on May 16 and took them until the 22, then had unprotected sex on the 24th, followed by 2 more weeks of active pills and then no withdrawal bleed? If that's correct, a test today should be accurate, but anything earlier could have been a false negative.

That said, skipping a withdrawal bleed doesn't signal pregnancy the way missing a period does - if you get pregnant on the pill you can still get a withdrawal bleed, although most people say it's lighter, later, and often browner (old blood). Not having a withdrawal bleed can just mean that your body didn't build much lining anyway, or the hormone drop didn't trigger a withdrawal for some obscure reason. It's pretty common on some brands of HBC and for some women.

All that said, IF the antibiotics interfered with your pills enough for your ovaries to wake up and you then ovulated sometime between the 24th and 29th, the sex on the 24th could have resulted in pregnancy. After the 29th you'd be safe again - on HBC seven days. I wouldn't think the chances are very high that you're pregnant, but it's possible.

[archangelbeth]

With respect, the drugstore.com site appears to be out of date and/or missing nuances. The most recent of their citations is the 2006 Mayo Clinic one, and I can't actually find anything resembling cite that agrees with their allegations about other antibiotics besides Rifampin affecting oral contraceptives.

(Except possibly the minipill page: http://www.mayoclinic.com/health/minipill/MY00991/DSECTION=what-you-can-expect )

I dug up some other reports, dating from 2001 and 2002, from PubMed (a .gov site; see my below post) which suggest that while some rare people may be affected by non-Rifampin antibiotics, the failure rate due to antibiotics is low enough to be subsumed into the expected general failure rate of oral contraceptives. (Which does mean it's worth saying that there is a rare failure rate, seemingly more dependent on the person than on the HBC or the antibiotic, of course -- but the drugstore.com site may be overstating the risk.)

I welcome more recent citations to trump the ones I found, of course! O:D

[gryphonwing.livejournal.com]

/bow

You did far better research than I did. Thank you - and now I know the real answer. :)