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Comment by chollida1 | Hacker News Reader

From the chart in the article I'm surprised the pill has such a poor performance record of 6-12 pregnancies out of 100 women.

When I was in high school, university and in my 20's almost all the women I knew were on the pill and I didn't hear once about an unplanned pregnancy or abortion.

Infact all the women I know joked about how they were surprised when they went off the pill how easy it was for them to get pregnant given that the pill had never failed them when they were younger.

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One thing is that this is not really 6-12 pregnancies out of 100 (possible pregnancies), it's 6-12 women out of 100 using the pill in a given year will get pregnant in that year, so it's pretty likely that even if the women you know had a similar distribution of use patterns as the average in the studies, there's a decent chance none of them would get pregnant. If you know 40 women and assume a 5% failure rate, there's still a (19/20)^40 = 13% chance that none of them would get pregnant.

Add to that that the people you know might be atypical in their use patterns. The "perfect use" failure rate for the pill is ~0.3%, which I take to mean that most of the pregnancies that occur on the pill are because someone forgot to take pills, that sort of thing.

Part of the performance record might well be due to not everyone taking the pill remembering to always take it. If you miss the odd day, I'd imagine that the chance of accidental pregnancy goes up a fair bit.

Also having to take it the same time every day, and the interaction between the pill and antibiotics. I've heard that many women don't realize that most antibiotics destroy the effectiveness of the pill, meaning that a back-up birth control method needs to be used in a cycle where she gets strep, or an ear infection, or a UTI, or many other common illnesses.

Yes, it was always my understanding that the 99%+ efficacy of oral contraceptives were based heavily on taking them in the manner prescribed.

I think those percentages are per year. So, out of 100 women, 6-12 will get pregnant within a year. That probably includes failure to actually take the pill, taking it with antibiotics, etc.

A girl I know got pregnant after taking the pill with antibiotics, or stopping it because of antibiotics and forgetting to mention that? Something like that.

keyword: "unplanned" - how many that did get pregnant did it with their fingers crossed?

The pill can be nerfed by interactions with other drugs. Modafinil, for example.

Well, Modafinil can lower the potency of the pill, but it doesn't totally ruin it -- especially if you take your pill at the same time each day, etc. I say this from personal experience. But yes, most people don't realize the impact other drugs can have on the pill.

That's probably typical use. Perfect use is is %99.9.

Indeed. When used correctly, the user should not ovulate on combined or dual hormone oral contraceptive.

Most studies show that a user can miss quite a few, such as 4 days in a row[1], and not ovulate.

[1] http://journals.lww.com/greenjournal/Abstract/1992/06000/Eff...

http://www.contraceptionjournal.org/article/S0010-7824(04)00...

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