How Effective Is Plan B Emergency Contraceptive In Preventing Pregnancy?

Posted on Thu, 8 Oct 2015

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Thu, 8 Oct 2015 Answered on

Fri, 30 Oct 2015 Last reviewed on

Question : Hello,

I’m wondering about the conclusiveness of a pregnancy test. I’ll go through the timeline of events based on days in the woman’s cycle.

On day 7 we had unprotected sex twice, using withdrawal. I urinated between the incidents to clear out semen.

On day 9 she took Plan B (<48 hours).

On days 16-18 she experienced period-type bleeding with some brown spotting afterwards, along with cramps in her abdomen and some in her lower back.

On day 24 she took a First Response pregnancy test, 30 min to an hour after urinating. Test was negative. Her cycles are typically 26-28 days, although her prior cycle was 21 days, possibly putting her at peak ovulation on the day we had sex.

I’d like to know, in your opinion, is this test conclusive? Of course the only way to know for sure is for her period to come again. In the time being, I’d like to know what you think.

Thank you.

Answered by Dr. Deepti Verma (17 minutes later)

Brief Answer:
Chances of pregnancy extremely low

Detailed Answer:
Hi dear, I have gone through your question and understand your concerns. Unprotected intercourse, even with withdrawal method, has a chance of pregnancy.
However, day 7 is considered to be safe for the intercourse in a 26-28 days cycle.
If she took plan B within48 hours of the sexual act, it is effective in preventing the pregnancy in 95-98% cases.
The bleeding she had on day 16-18 is likely to be the withdrawal bleeding due to the hormonal effect of plan B.
First response test is conclusive, however sometimes false negative can occur.
I would suggest her to repeat her urine pregnancy test at least one week after her next expected periods, to confirm the diagnosis.
Hope you found the answer helpful. Please do get back for further queries.
Wishing you good health.
Regards
Dr Deepti Verma

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Deepti Verma (47 hours later)

Thank you for your response. She went to the doctor today (day 27) and did some type of urine test where they put it in a machine and it came back negative. I'm not sure what type of test it was, can you shed any light on that?

Answered by Dr. Deepti Verma (3 hours later)

Brief Answer:
Test for beta hCG

Detailed Answer:
Hi dear, the urine test she had undergone is most likely the card test for detecting the pregnancy hormone beta hCG.Regards
Dr Deepti Verma

Above answer was peer-reviewed by : Dr. Vinay Bhardwaj

Follow up: Dr. Deepti Verma (10 hours later)

Thank you. I figured it was an hcg test. Are those tests more sensitive/accurate than the home tests?

Answered by Dr. Deepti Verma (44 minutes later)

Brief Answer:
Yes

Detailed Answer:
Hi dear, yes they are more accurate than home test.
Regards
Dr Deepti Verma

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Deepti Verma (15 minutes later)

Okay, thank you. That is good news. Accurate enough to be conclusive?

Just to clarify, it was a urine test, not a blood test. Thank you.

Answered by Dr. Deepti Verma (1 hour later)

Brief Answer:
It is conclusive

Detailed Answer:
Yes dear, I mentioned that they had checked beta hCG in the urine. It is a very sensitive test. It is conclusive of the fact there is no pregnancy.
Regards
Dr Deepti Verma

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar