OCP Ovulation Risks: Missed Pills vs Blank Pills

[JeSuisPA]

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This concept still confuses me. With an oral contraceptive pill pack, the pills at the end are blank. Effectively, the woman is skipping her hormone pills for 4 days or so depending on the pack. How is this different from her missing one pill in terms of ovulation/pregnancy risk? I was taught that missing 1-2 pills creates a decent chance for ovulation, so obviously she should be advised to use backup methods. How are those 1-2 days different from first 1-2 days of her blank pills?

And a followup- if the patient chooses to do prolonged cycles, in theory would it matter the timing during her 90 day cycle when she chooses to have her period/take the blanks?

I hope I've made my question clear. I'm sure this must be explained somewhere and obgyn is not my specialty, so thanks for your help explaining it.

 

[307Doc]

Birth control works only if taken. If pills are missed then back up should be considered.

 

[JeSuisPA]

Birth control works only if taken. If pills are missed then back up should be considered.

Obviously. That doesn't answer any of my questions.

 

[THP]

This concept still confuses me. With an oral contraceptive pill pack, the pills at the end are blank. Effectively, the woman is skipping her hormone pills for 4 days or so depending on the pack. How is this different from her missing one pill in terms of ovulation/pregnancy risk? I was taught that missing 1-2 pills creates a decent chance for ovulation, so obviously she should be advised to use backup methods. How are those 1-2 days different from first 1-2 days of her blank pills?

And a followup- if the patient chooses to do prolonged cycles, in theory would it matter the timing during her 90 day cycle when she chooses to have her period/take the blanks?

I hope I've made my question clear. I'm sure this must be explained somewhere and obgyn is not my specialty, so thanks for your help explaining it.

That's a really good question and I'm glad you are thinking about the mechanism of action of medications.

To answer your first question, missing a pill here or there is probably not going to affect its effectiveness in a patient who has been on the pill for several months. In the setting of a new start on a pill there might already be follicular recruitment and missing a few pills at the crucial time could lead to ovulation.

OCPs are primarily progestational in effect. The estradiol serves to inhibit FSH production and thus sometimes prevent ovulation. When you stop a pill for more than a few days 2 things happen: the endometrium sloughs because of progestin withdrawal and follicles start to develop because of the missing estradiol. If you are only missing 4 or 5 days of pills that is usually not enough time to get to the point of ovulation. If you are skipping pills you will also probably have breakthrough bleeding. Of course we tell patients to take the pill every day as directed so that there aren't any failures and I suspect that when failures do occur its because of very sporadic use of the pill. Or the dose may not be high enough to suppress the normal menstrual cycle as not all women are the same.

There is a really nice chapter in Speroff REI text (chapter 22) with lots of details about OCPs. If your hospital subscribes electronically, its a very valuable read. It quotes several small studies which showed that skipping 4 consecutive pills at varying times in the cycle did not result in ovulation and when women increase the pill free interval up to 11 days we still don't see signs of ovulation. Granted these are small studies. Even the lowest dose estrogen pills (lo-loestrin) seem to effectively prevent ovulation. Speroff notes that most failures are related to episodes of gastroenteritis. The recommendations for backup contraception during missed pill cycles are being conservative but is probably also wise.

As far as your second question goes, based on the above, no it doesn't matter when your pill free interval is in a 90 continuous OCP regimen. I would recommend you follow the instructions though so you don't forget for extended periods of time.

 

[JeSuisPA]

Thank you, that was an excellent explanation!