Pregnancy Risks After Unprotected Sex and Emergency Contraception

Is the probability of getting pregnant high?

I had sexual intercourse with my girlfriend recently.
Although we did not use a condom, there was no ejaculation inside.
Later, I realized that it was likely during her fertile window.
Five days after the incident, she took Ella.
Will the contraceptive effect still be effective? Additionally, she received the BNT vaccine the day after the incident.
Will this affect the contraceptive effectiveness? What is the likelihood of pregnancy?

Niming, 10~19 year old female. Ask Date: 2022/05/31

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, based on your description, the pregnancy rate after taking ulipristal acetate (ella) between 48 to 120 hours is 2.1%.
It is advised to check for pregnancy if your period is more than a week late.
Thank you! Wishing you peace and health.
Dr.
Chang

Reply Date: 2022/05/31

More Info

When it comes to understanding pregnancy risks after unprotected sex and the use of emergency contraception, there are several factors to consider. Based on your description, you had unprotected sex during what you suspect was a fertile period but did not ejaculate inside your partner. You took the emergency contraceptive pill (ella) five days after the incident. Let’s break down the situation.

Effectiveness of Emergency Contraception
Ella (ulipristal acetate) is a type of emergency contraceptive that is effective when taken within 120 hours (5 days) after unprotected intercourse. It works primarily by delaying ovulation. If ovulation has already occurred, its effectiveness may be reduced. Since you took ella five days after the sexual encounter, its effectiveness would depend on whether ovulation had already taken place. If ovulation was imminent or had already occurred, the chances of preventing pregnancy would be lower, but it is still more effective than not taking any emergency contraception at all.

Timing and Fertility
The "danger period" or fertile window typically occurs around the time of ovulation, which is usually about 14 days before the start of the next menstrual period. If your girlfriend has irregular cycles, pinpointing ovulation can be more challenging. If you had unprotected sex close to ovulation, the risk of pregnancy is higher, even if ejaculation did not occur inside the vagina, as pre-ejaculate fluid can contain sperm.

Interaction with Vaccination
Regarding your girlfriend receiving the BNT (Pfizer-BioNTech) vaccine the day after taking the emergency contraceptive, there is no evidence to suggest that receiving a COVID-19 vaccine affects the efficacy of emergency contraception. Vaccines work by stimulating the immune system and do not interfere with hormonal contraceptives or emergency contraceptives.

Pregnancy Risk Assessment
Given that you had unprotected sex during a potentially fertile period and took ella afterward, the risk of pregnancy exists but is mitigated by the use of emergency contraception. However, since you took it five days later, the risk is not negligible. If your girlfriend experiences a missed period or unusual symptoms (like nausea, breast tenderness, or fatigue), it would be prudent for her to take a pregnancy test.

Conclusion
In summary, while taking ella five days after unprotected sex may reduce the risk of pregnancy, it is not guaranteed, especially if ovulation had already occurred. The administration of the BNT vaccine does not impact the effectiveness of the emergency contraceptive. If there are any concerns about potential pregnancy or if her menstrual cycle is delayed, it is advisable for her to take a pregnancy test and consult with a healthcare provider for further guidance. Regular use of reliable contraception in the future can help prevent similar situations and provide peace of mind.

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