Snopes says otherwise. Even if Snopes is mistaken, that kind of fluctuation could result from a power outage interfering with the responsible use of birth control. Can't find your pills in the dark? Don't want to go out when all the streetlights are off to run to the drugstore for condoms? Meh, don't let that stop you.

I think that individuals are probably very likely to have the wrong amount of sex, but it is my suspicion that on average we're doing okay.