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On OCP but fearing pregnancy due to antibiotic use

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My girlfriend and I have been dating for about 9 months now. I'm 24 and she is 21. She has been on birth control since the age of 15. She was on the shot from age 15-19 and then went to birth control pills just after the age of 19. She has been on birth control pills since. She is very good at taking her pills and not missing, as well as taking them at the same time each day (within the 2-3 window period). She does not miss her pills or anything of such. She does a pretty good job with that. Over the last two and a half months she had her BC dosage upped and put on a higher dosage. The doctor told her that she would have some side effects etc. She usually gets her period around the same time each month, give or take a day or two. She just had a urinary traction infection about three weeks ago. She was given antibiotic to take for three days. We did not have sexual intercourse while she had the 3 day antibiotic, but once she got off the antibiotic (took all of the medication) we started having sexual intercourse again. This would have been about 2.5 weeks ago. Unfortunately, we do have unprotected sex and we do not use protection. I know that is not a good practice whether you are on BC or not. I usually do not ejaculate inside of her but I did this past Thursday night and she was expecting to get her period a day or two after that. It is now Monday and she still has not gotten her period. We took a pregnancy test two week ago and it was negative (not really sure why we did then, but she wanted to make sure because of the UTI infection. She still has some of the placebo pills left on her cycle of pills for this month. My understanding is these are the pills that you do NOT have to take, but she does always take them to stay on track and just to be safe. I have read that you are not considered late until you finish all of the pills, but I have also read differently. I'm also confused about the ovulation thing. I have read that when you are on BC pills that you do not ovulate so it is hard to get pregnant, but have also heard that you do. I guess my biggest question is do you feel she is at a higher risk because of the UTI infection and because of me going inside of her a few days before she was expecting her period or what? We are both kind of freaking out about this. I know that stress can cause female to make her menstrual cycle late or even miss. What should I think at this point and what should I do next? Honest opinion. We thought about taking another pregnancy test tonight...Please any help would be great.

Category: Family Physician-GP

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Category: Infertility Specialist
 19 Doctors Online


Thank you for your query at

Firstly, you are not considered late until you finish ALL of the pills ( including the placebo ones ).

It would be clearer to me if you mention the EXACT date of her last menstrual period, and the general cycle length.

As she is still on the placebo pills, she is not late going by the pattern of birth control pills.

When you are on BC, you do not ovulate ( mostly speaking ).
Birth control is 99 % effective as a contraceptive, and it acts as a contraceptive, by interfering with ovulation. The fact that it is 99 % effective, and not 100 % , means that SOMETIMES, albeit rarely, ovulation CAN occur while on BC.

Some antibiotics do interfere with the pills, reducing their efficacy -a specific name would help me guide you better, which particular antibiotic was prescribed, however it was for only 3 days, and as long as she took the pills sincerely for the whole pack, on the whole, she stays protected.

Ejaculation inside the vagina a day or two before the expected period has LESS chances of pregnancy, chances are maximum mid cycle, when ovulation occurs, if at all it does, while on BC.

Stress CAN cause delayed periods - as can anxiety, hectic travelling, change of climate or altitude, thyroid disorders, polycystic ovaries etc, and once in a while a delayed period might be just that - a delayed period, without any other implications, as long as it is a one off event, not a pattern. I would not worry right now.

Going by what you have described, she is diligent with taking BC, and chances of pregnancy ( honest opinion ) in my view are quite low.

You should repeat a pregnancy test ( you know that the one you took was too early , and hence irrelevant ), and that should be done once she finishes with her placebo pills, starts her new pack for a couple of days, and still fails to have a period.

I hope this answer helped you. All the best. I would be happy to address any follow up questions.

Take care.
Yes, protected sex is best for both of you, BC notwithstanding.

Dr. Aarti Vazirani
Category: Infertility Specialist
Residency: Obstetrics & Gynecolog, BJMC,Civil hospital, Ahmedabad, 2008
Post Graduate: MS (Obstetrics & Gynecology), B.J. Medical College, Ahmedabad, 2008
Medical School: MBBS, B.J. Medical College, Ahmedabad, 2004
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