How often would I ovulate while taking the BC pill and be relying on the other factors (e.g uterine lining changes) to avoid pregnancy ?
Specifically, tri-phasic combination birth control pills (I’m on Levlen ED)
I’ve found pro-life sites which say up to 27% rate of ovulation, I’ve found sites that say it is immeasurable, and others which don’t quantify it, just state that it’s “rare”.
This is rather an important question to me, so I’d appreciate any help. What’s the Straight Dope ?
I was told that ovulation didn’t occur if the pill was taken properly (ie same time every day, not missing days, etc). I suppose the 1 or 3% error rate or whatever that percentage is would be the relative amount of women who obviously DID ovulate (once statistical analysis removed all the other factors), since they became pregnant while taking the pill. If you use additional methods to avoid pregnancy, I imagine you’d have a less than 1% chance of pregnancy, probably less.
And remember what our high school teachers always said? The only 100% way to avoid getting pregnant is to not have sex! 
Well, there are other ways too, but they are kind of drastic.
Here’s what my doc told me: Ovulation might occur up to 5% of the time, particularly if the pill is not taken within the same two-hour window each day, but the pill also works by thickening the cervical mucus to prevent fertilization of the egg and implantation of a fertilized egg in the uterus.
Sounds like a triple-approach, to me. And even with the pill alone, if it’s taken properly, failure rates are miniscule. (Unless it happens to you, I suppose…) But pill + another method of birth control is probably as fool-proof as it gets.
O.K, so we have 1-3% and 5%, both second hand reports. I appreciate you both sharing your knowledge, though I am looking for something a little more solid than a GP’s comment.
Has anybody studied this ? Is there any scientific data out there about this ?
I ask because I will soon be undergoing a tubal occlusion procedure. This is where the tubes are blocked over a period of 3 months (or possibly a little more) by growing tissue. With this blockage developing, sperm will be able to get through much easier than an egg would. I’m concerned about the chance of ovulating and having an ectopic pregnancy occur before the tubes are completely blocked. My doctor has said “it should be fine” which isn’t the most reassuring thing I’ve heard, and so I would like to know what my actual risk is for those few months.
Surely someone has studied exactly how the pill works and how effective each action is ?