Missed Period After Emergency Contraceptive: What's the Chance of Pregnancy?

I took emergency contraception, but my period hasn't arrived yet?

I would like to ask about my girlfriend's menstrual cycle.
Her last period was from July 10 to July 15.
We had unprotected intercourse on August 1, and I accidentally ejaculated inside her.
She took emergency contraception within 5 hours after that.
After taking the pill, she experienced nausea and dizziness for about 4 to 5 days, but she did not feel like vomiting.
Today is August 10, and her period has not arrived yet, a week later.
What is the likelihood of her being pregnant?

Yi, 20~29 year old female. Ask Date: 2023/08/10

Dr. Lin Manying reply Obstetrics and Gynecology

Hello, please take a pregnancy test first.
Hualien Hospital, Ministry of Health and Welfare, cares about your health.

Reply Date: 2023/08/10

More Info

When it comes to missed periods after taking emergency contraception, it’s important to understand how these medications work and the factors that can influence menstrual cycles. Emergency contraceptive pills (ECPs), such as Plan B or Ella, are designed to prevent pregnancy after unprotected intercourse or contraceptive failure. They are most effective when taken as soon as possible after the incident, ideally within 72 to 120 hours, depending on the specific medication used.

In your case, your girlfriend took the emergency contraceptive within five hours of unprotected intercourse, which is a timely response and significantly reduces the chances of pregnancy. However, it’s important to note that ECPs can cause temporary hormonal changes that may affect the menstrual cycle. Common side effects of ECPs include nausea, fatigue, and changes in the timing of the next menstrual period. The nausea and dizziness your girlfriend experienced for several days after taking the pill are typical side effects and can be attributed to the hormonal fluctuations caused by the medication.

Regarding the missed period, it is not uncommon for women to experience a delay in their menstrual cycle after taking emergency contraception. The hormonal changes can lead to a cycle that is longer or shorter than usual, and in some cases, it can cause a missed period altogether. It’s also worth noting that stress, changes in weight, and other factors can also contribute to menstrual irregularities.

As for the likelihood of pregnancy, since your girlfriend took the emergency contraceptive promptly, the chances are relatively low. However, no contraceptive method is 100% effective, and there is still a small possibility of pregnancy. If her period does not arrive within a week or so, it would be advisable for her to take a home pregnancy test for confirmation. These tests are generally accurate when taken after a missed period.

If the test is positive, it would be important for her to consult with a healthcare provider to discuss the next steps. If the test is negative and her period still does not arrive, she may want to consult a healthcare provider to rule out any other underlying issues or to discuss her menstrual cycle and any concerns she may have.

In summary, while the chances of pregnancy after taking emergency contraception are low, it is not impossible. The missed period could be a result of the hormonal effects of the emergency contraceptive. Monitoring her menstrual cycle and taking a pregnancy test if her period does not arrive soon will provide clarity on her situation. If there are any further concerns or unusual symptoms, seeking medical advice is always a prudent step.

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