Is Plan B Effective While Ovulating & Signs That It Didn’t Work

Plan B, also known as the morning-after pill, is an emergency contraceptive pill that is used to prevent pregnancy after unprotected sex. 

It contains a hormone called levonorgestrel and is more effective within 72 hours of unprotected sex.

Plan B can help prevent pregnancy after unprotected sex if you weren’t already on birth control, if you missed a dose of your birth control pill, if your birth control method failed, or if you were sexually assaulted.

The morning-after pill helps prevent pregnancy by delaying ovulation (release of an egg from the ovaries). 

But what if you have unprotected sex while ovulating? Does plan B work during ovulation? 

We answer this and many other questions about Plan B in this article.

Does Plan B work during ovulation?

Various studies have shown that morning-after pills work by delaying ovulation. Therefore, Plan B will not work if it’s taken after ovulation has already happened. 

Some believe that the pill may have post-ovulatory effects, such as preventing fertilization (union of the egg and sperm). However, studies have discounted this and shown that Plan B has little or no effect after ovulation occurs.

The pill works best if taken before ovulation, and its probability of failing increases as you approach ovulation.

Signs that Plan B didn’t work

1) Missed Period

If a woman’s period doesn’t arrive as expected after taking Plan B, it may indicate that the emergency contraceptive did not work.

2) Ovulation Symptoms

If there are signs of ovulation, such as cervical mucus changes or ovulation pain, it suggests that the egg was released, and Plan B may not have prevented ovulation.

3) Pregnancy Symptoms

Early signs of pregnancy, like breast tenderness, nausea, or fatigue, may appear, indicating Plan B may not have been effective.

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Can the morning-after pill delay ovulation?

Yes. The morning-after pill works best by delaying ovulation for up to five days.

This means there is still a possibility that you may become pregnant after taking the pill if you go on to have unprotected sex before your next period.

Delaying ovulation after unprotected sex can help prevent pregnancy because:

  • Sperm can live for up to five days in the uterus and the fallopian tubes. So, if you have unprotected sex close to your ovulation, there might still be sperm present to possibly fertilize an egg as soon as you ovulate.
  • The egg itself can stay within the fallopian tubes for up to 24 hours after ovulation. Therefore, if you delay ovulation, the sperm would most likely die before the egg is released.  

What happens if you take the morning-after pill while ovulating?

Since it is designed to delay or prevent ovulation, there will be little to no effect on pregnancy risk if the morning-after pill is taken while you are ovulating.

The morning-after pill may delay your period by about a week. If your period doesn’t return within three to four weeks after taking the pill, you should take a pregnancy test.

Also, you should contact your healthcare provider if you have spotting or vaginal bleeding that lasts longer than a week or if you have severe lower abdominal pain within three to five weeks after taking the morning-after pill.

How do you know when you are ovulating?

Knowing your ovulatory period can be tricky. Here are some possible signs you may notice and tests you can carry out to help you identify ovulation:

1) Increased libido

You may realize that you feel more in the mood for sex when ovulation is approaching. This is a normal biological response.

2) Tender breasts

Swollen and tender breasts can occur during ovulation due to the rising estrogen levels in the body.

3) Cervical mucus

Cervical mucus becomes progressively more slippery and transparent (resembling raw egg whites) in the days leading up to ovulation or during ovulation. 

You may notice this mucus in your underwear or when you go to the bathroom. The mucus helps sperm easily move through the cervix.

4) Elevated basal body temperature

Basal body temperature (BBT) usually remains consistent until just before ovulation, when it will reduce slightly. It then spikes back up and remains elevated, a sign that ovulation has occurred.

5) Ovulation pain

You may notice a sharp or cramping pain on one side of your lower abdomen during ovulation. It occurs because of irritation caused by an egg breaking away from the ovary.

6) Ovulation test

Ovulation test strips are an affordable and easy way to confirm ovulation. The strips detect the amount of luteinizing hormone in your urine, which is an indicator that ovulation is about to happen or is happening.

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How likely is it to get pregnant while ovulating?

The chances of getting pregnant if you have unprotected sex on your day of ovulation are about 20%. 

The chances are higher if you have unprotected sex on the days leading up to ovulation at 27% to 41%.

How to prevent pregnancy during ovulation

The current standard methods that are available to prevent pregnancy aren’t meant to be used specifically during ovulation. They are designed to provide a long-term solution to pregnancy prevention throughout your cycle. 

These methods include:

Long-acting reversible contraceptives

These allow you to prevent pregnancy for multiple years. They include:

  • Copper intrauterine device – contains copper that acts by killing sperm and preventing them from reaching the egg.
  • Hormonal intrauterine device – contains hormones that have various effects, such as causing the mucous in your cervix to thicken, which helps prevent sperm from reaching the egg.
  • The implantable rod – is a thin hormone-filled rod that is inserted under the skin on the inside of your upper arm.

Contraceptive shots

These are injections that contain hormones. They are given at intervals of one to three months.  

Short-acting hormonal methods

These function by preventing the ovaries from releasing eggs and preventing the sperm from reaching and fertilizing an egg. They include:

Barrier methods

Their primary function is to prevent sperm from reaching the egg. Some of them have dual protection as they also help to prevent HIV and other sexually transmitted infections (STIs).

The CDC encourages individuals to consider birth control methods that offer dual protection when deciding on how to prevent pregnancy. The barrier methods include:

When do you need to take plan B for it to work?

The morning-after pill can be taken up to five days after having unprotected sex, but it works best if it is taken during the first three days. It helps reduce the risk of getting pregnant by up to 89% when used the right way. 

Consult with your healthcare professional for guidance on its usage.

It is important to note that plan B is not as effective as regular contraception, so it shouldn’t be used as a substitute for routine birth control.

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Does plan B affect your fertility?

There is currently no evidence that plan B can affect your future fertility, regardless of how many times you use it.


  • Plan B is a contraceptive option that should only be used in emergency cases and not as a routine method of contraception. 
  • Being on a proven method of routine contraception will remove the need for the morning-after pill. 
  • That way, you don’t have to think about whether the pill worked or not because you were ovulating.  
  • To make an informed decision, speak with your doctor about reliable forms of contraception that are available. 
  • If you used plan B and you aren’t sure whether it worked or not, have a pregnancy test done three weeks later to be certain.

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  1. Gemzell-Danielsson K, Berger C, P G L L. Emergency contraception — mechanisms of action. Contraception. 2013 Mar;87(3):300-8. doi: 10.1016/j.contraception.2012.08.021. Epub 2012 Oct 29. PMID: 23114735.
  2. Novikova N, Weisberg E, Stanczyk FZ, Croxatto HB, Fraser IS. Effectiveness of levonorgestrel emergency contraception given before or after ovulation–a pilot study. Contraception. 2007 Feb;75(2):112-8. doi: 10.1016/j.contraception.2006.08.015. Epub 2006 Oct 27. PMID: 17241840.
  3. Shohel M, Rahman MM, Zaman A, Uddin MM, Al-Amin MM, Reza HM. A systematic review of effectiveness and safety of different regimens of levonorgestrel oral tablets for emergency contraception. BMC Womens Health. 2014 Apr 4;14:54. doi: 10.1186/1472-6874-14-54. PMID: 24708837; PMCID: PMC3977662.

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