Take a free contraceptive test at BestMethodForMe.com
Managing Contraception Questions and Answers
Questions & Answers
Everything you ever wanted to know about managing contraception and weren't afraid to ask.

Click here to ask a question
Search the Questions & Answers Browse by Category
<< Return to questions

I have had only one Depo injection and am having unprotected sex. Could I be pregnant? #106/9
I am 23 years old with a wonderful 2 year old. I took my first Depo shot on October 3rd and was due between Dec 19 - Jan 2nd. I have been having unprotected sex with my boyfriend the last time was Christmas, I believe. I spotted right around the 19th and we had sex then too.

Is it lkely I could be pregnant. If so, how likely is it? This was only my first shot and unsure of how well the first one really works.

Depo was started October 3rd and the next shot was due at the end of December.  You have been and still are (as of January 7th) protected from that first injection.


It is now demonstrated that Depo may be taken as long as 13 + 4 weeks or 17 weeks apart according to the World Health Organization.


Effectiveness of Depo-Provera:


DMPA-IM is in the second tier of contraceptive effectiveness.  With correct and consistent use, the probability pf pregnancy is only 0.3%.  With typical use the failure rate is 8%.  These estimates apply to an 11-13 week regimen, with each injection providing 150 mg DMPA per 1 cc.


The perfect use estimate for Depo-Provera is the weighted average of the seven studies of the 150 IM mg dose.  These trials yield an estimate of efficacy during perfect rather than typical use because either women late for an injection were discontinued or all pregnancies reported occurred during actual use (after one injection but before the next was scheduled).  In two large trials of DMPA-SC, there were no reported pregnancies during perfect use in either study; a typical-use pregnancy rate is not available, since pregnancy was defined as a positive pregnancy test prior to the next scheduled injection.  It is unlikely that DMPA-SC never fails, so we set the pregnancy rate during perfect use.  It is possible that DMPA-SC has higher efficacy than DMPA-IM during perfect use, but the company that markets both products has made no such claim.   


Her reply on 1-8: “Okay, thank you so much.  I actually just started my full period the other day, so I know I’m not pregnant.  Just don’t have insurance right now due to a switch in jobs so I wanted some information.  I thank you very much for the help and will definitely be using protection until I do get the second shot.”


Thank you!


Key Words:  Depo-Provera shot, unprotected sex, pregnant, protected, World Health Organization, effectiveness



Goldberg AB, Grimes DA. Injectable contraceptives IN Hatcher RA, Trussell J. Nelson AL et al Contraceptive Technology 19th edition: page 158, Ardent Media Inc. 2008


Trussell J. Contraceptive efficacy IN Hatcher RA, Nelson AL, Cates Jr. W. et al Contraceptive Technology 19th edition, page 753; Ardent Media Inc. 2008

Posted 2-4-2009, Updated 2-6-2009, Updated 2-25-2009 

Robert A. Hatcher MD, MPH
Emeritus Professor of Gynecology and Obstetrics
Emory University School of Medicine
Atlanta, GA

The directors and owners of this website and any publications and information concerning health matters offered here advise a person with a particular problem to consult a primary-care clinician or a specialist in obstetrics, gynecology, or urology (depending on the problem or the contraceptive) as well as the product package insert and other references before diagnosing, managing, or treating the problem.
Visitor Comments
No visitor comments posted.

Post a comment
Post Comment
To post a comment for this question, simply complete the form below. Fields marked with an asterisk are required.
   Your Name:
   Email Address:
* Your Comment:
* Enter the code below:
Related Questions
No related questions were found.
No attachments were found.

Suggestions, recommendations, questions, comments, data from the literature, interpretation of laboratory tests and other information provided on this site are for informational purposes only and are not intended to be relied upon as advice from or implied to be a substitute for the professional advice of a physician, nurse practitioner, nurse midwife, counselor or other healthcare professional. Always seek the advice of your clinician or other professional for any questions you may have regarding your health, medical condition, method of birth control and other family planning or personal/social issues. Periodic references to costs of birth control methods on this website are estimates only and your actual cost for any specific method of birth control may be more or less than the stated amount. Emory University School of Medicine, Bridging the Gap Foundation, and Bridging the Gap Communications Inc are not responsible for any damage or loss you may incur as a result of your use of or reliance on any material or information provided through this website.