How Effective Is Plan B Emergency Contraceptive In Preventing Pregnancy?

Posted on Wed, 11 Nov 2015

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

Wed, 11 Nov 2015 Answered on

Thu, 3 Dec 2015 Last reviewed on

Question : I had unprotected sex 18 hours after taking plan B. I spoke to a nurse who said it will still work because it was same day. Also, i was ovulating. Is this true?

Answered by Dr. Srilatha Myaka (51 minutes later)

Brief Answer:
plan B is effective

Detailed Answer:
Hello dear,welcome to healthcare magic.I have gone through your query.
I understand your concern.Iam Dr.Srilatha gynaecologist.
In my opinion the plan B or emergency contraception is effective in 95% of cases if taken 72 hours of unprotected sex.
It is a high dose of progesterone which works in 3 different ways:-
1)It prevents ovulation.
2)It inhibits fertilisation by thickening the cervical mucus.
3)By inhibiting the implantation.
So depending on the stage of the cycle it works.
As you have taken the plan B within stipulated time the chance of pregnancy is rare.
But unprotected sex after plan B might again pose to risk for pregnancy.And though it was taken on the same day the protection from pregnancy might be doubtful.
And as you are around the ovulation period the risk might be more.
In order to be safe another dose of plan B might be taken.
Hope this satisfies your query.
Feel free to discuss furthur.Iam always there to answer you in case if needed.
Best regards....Dr.Srilatha

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

Follow up: Dr. Srilatha Myaka (1 hour later)

I understand, thank you. So still, because it was after i took the pill but within the same day, would you say I'm at high risk for pregnancy or just moderatelly.

Answered by Dr. Srilatha Myaka (6 hours later)

Brief Answer:
Risk cannot be predicted

Detailed Answer:
Hello dear,I have gone through your query.
In my opinion we cannot grade as high or moderate risk in this scenario.
Ipill is an emergency contraception which offers protection only once mostly.
Intercourse after ipill intake might pose risk for pregnancy.
The ipill acts at 3 stages as I explained you in previous query.
Ipill failure rate is more around the ovulation
period ie.,around 2-5%.So as you are around the ovulation there might be risk.
Though intercourse was done within 18 hours of intake of ipill the protection can't be predicted.
So another dose of ipill can be taken to be on the safer side.
This type of frequent intake should also not be done under regular basis.For regular basis contraception should be followed like condom,hormonal pills etc.
Hope this satisfies your query.
Feel free to discuss furthur.
Best regards...Dr.Srilatha

Above answer was peer-reviewed by : Dr. Sonia Raina