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Updated: Jun 2, 2026
12:29
Population and Single-Cell Analysis of Antibiotic Persistence in Escherichia coli
Published on: March 24, 2023
Antibiotics and oral contraceptive failure - a case-crossover study
Sengwee Toh1, Allen A Mitchell, Marlene Anderka
1Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston, MA 02215, USA. darrentoh@post.harvard.edu
Contraception
|April 12, 2011
Summary
This study found no significant link between antibiotic use and combined oral contraceptive (COC) failure, meaning pregnancy risk was not elevated. However, the research had limitations, so an increased risk cannot be entirely ruled out.
Area of Science:
- Reproductive Health
- Pharmacoepidemiology
- Drug Safety
Background:
- Controversy exists regarding the association between antibiotic use and combined oral contraceptive (COC) failure.
- This study aimed to investigate the risk of breakthrough pregnancy in women using COCs concurrently with antibiotics.
Purpose of the Study:
- To examine the effect of concomitant antibiotic treatment on the risk of breakthrough pregnancy among combined oral contraceptive (COC) users.
Main Methods:
- A case-crossover study design was employed, analyzing data from 1330 COC failure cases and 25,941 controls.
- Self-matched odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression.
- A case-time-control analysis was also conducted using non-users of COCs with unplanned pregnancies as controls.
Main Results:
- For the combined data, the self-matched OR was 1.08 (95% CI: 0.63-1.84) and the case-time-control OR was 1.12 (0.63-1.98) for overall antibiotic use.
- Adjusting for varying characteristics between case and control periods did not significantly alter the results.
- In the National Birth Defects Prevention Study (NBDPS) cohort, a 1-month gap between periods yielded a self-matched OR of 1.45 (0.85-2.50) and a case-time-control OR of 1.55 (0.86-2.79) for overall antibiotic use.
Conclusions:
- No association was found between concurrent antibiotic use and breakthrough pregnancy risk in combined oral contraceptive (COC) users.
- Due to limited statistical power and potential carryover effects, the study cannot definitively exclude an elevated risk of COC failure in women using antibiotics.
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