Oral Contraceptives: Pregnancy Risks and Effectiveness Explained

Oral contraceptives

Hello, doctor.
I have been taking the 21-day oral contraceptive pill (yellow pill) for several months, consistently taking it on the fifth day of my menstrual cycle, regardless of the interval between cycles.
Occasionally, I take it for a few extra days or start a new pack to delay my period, so my menstruation is not regular each month.
I would like to ask about my recent medication.
Since the clinic I usually visit was closed, I bought the 28-day oral contraceptive pill at the pharmacy on the fifth day of my period.
I took one pill on April 5, and the next day when the clinic reopened, I went to see the doctor and received my usual 21-day contraceptive pill, resuming the 21-day regimen.
Since April 9, I have had unprotected sexual intercourse with ejaculation, and my menstrual tracking app indicates that my ovulation period is on April 16.
I would like to know if there is a possibility of pregnancy.
Is the likelihood high or low? Additionally, I would like to inquire about the mechanism of action of oral contraceptives.
Many sources state that it takes seven days of consistent use to fully suppress ovulation for effective contraception.
Since I have been taking the pill for several months, does this mean that I need to take each pack for seven days every month to maintain sufficient contraceptive efficacy, or does the seven-day guideline only apply to the first pack of the oral contraceptive when using it for the first time?

Nian, 20~29 year old female. Ask Date: 2018/04/15

Dr. Huang Jianzhong reply Obstetrics and Gynecology

I have been taking the 21-day oral contraceptive (yellow pill) consistently for several months, always starting on the fifth day of my menstrual cycle, regardless of the number of days since my last period.
Occasionally, I take extra pills or start a new pack to delay my period, so my menstrual cycle is not regular.
I would like to inquire about my recent medication use.
Since the clinic I usually visit was closed, I bought the 28-day oral contraceptive from a pharmacy on the fifth day of my period.
On April 5, I took one pill, and the next day when the clinic reopened, I went to see the doctor and got back on the original 21-day contraceptive, continuing to take it as prescribed.
Since April 9, I have had unprotected sexual intercourse with ejaculation, and my menstrual tracking app indicates that my ovulation period is on April 16.

1.
Is there a possibility of pregnancy? Is the likelihood high or low?
Answer: It is unlikely that you are pregnant.
2.
The purpose of the contraceptive pill is to suppress ovulation.
Many sources state that it takes a full 7 days of consistent use to achieve the effective dosage for complete ovulation suppression.
However, I have been taking it for several months.
I would like to know if I need to take each pack for seven days every month to ensure adequate contraceptive effectiveness, or does the seven-day rule only apply to the first pack of the contraceptive pill?
Answer: The seven-day rule applies to the first pack of the contraceptive pill during initial use.

Reply Date: 2018/04/15

More Info

Understanding oral contraceptives and their effectiveness is crucial for anyone relying on them for pregnancy prevention. In your case, you've been taking the "温不妊" (Wenbu Ning) 21-day oral contraceptive pill consistently for several months, which is a positive factor in maintaining contraceptive efficacy. However, there are several aspects to consider regarding your recent changes in medication and the potential for pregnancy.

Firstly, oral contraceptives work primarily by suppressing ovulation, thickening cervical mucus, and altering the uterine lining to prevent fertilization and implantation. When taken correctly, they are highly effective, with typical use showing a failure rate of about 7% per year, while perfect use can reduce this to less than 1%.
Regarding your specific situation, you mentioned switching from the 21-day pill to the 28-day pill and then returning to the 21-day regimen. The key point here is that as long as you have been taking your oral contraceptives consistently and correctly, the risk of pregnancy remains low. However, there are a few caveats:
1. Switching Pills: When you switched to the 28-day pill and then returned to the 21-day pill, it is essential to ensure that you did not miss any doses. If you took the 28-day pill for only one day and then returned to the 21-day pill without missing any doses, your contraceptive protection should still be intact. However, if there was any gap in taking the pills or if you missed doses, this could increase the risk of ovulation.

2. Timing of Intercourse: You mentioned having unprotected intercourse during your estimated ovulation period (April 16). If you were taking your contraceptive pills correctly leading up to this date, the likelihood of ovulation occurring is significantly reduced. However, if there were any inconsistencies in your pill-taking, this could potentially lead to ovulation and increase the risk of pregnancy.

3. 7-Day Rule: The guideline stating that it takes 7 days of consistent pill-taking to achieve full contraceptive efficacy generally applies to the first cycle of starting a new oral contraceptive. Since you have been on the pill for several months, this rule is less critical for you unless you have missed doses or switched brands.
In summary, if you have been diligent in taking your oral contraceptives without missing doses, the risk of pregnancy is low, even if you had intercourse during your estimated ovulation period. However, if you are concerned about the possibility of pregnancy, consider taking a home pregnancy test if your period is late or consult with your healthcare provider for further evaluation and guidance.

It's also worth noting that if you ever feel uncertain about your contraceptive method or experience any side effects, it's always best to consult with a healthcare professional. They can provide personalized advice based on your health history and current situation. Remember, while oral contraceptives are effective, no method is 100% foolproof, and understanding how to use them correctly is key to maximizing their effectiveness.

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