If you want to get a high school health class educator nervous, just bring up the topic of coitus interruptus (CI), the idea that the man should withdraw from the woman just prior to ejaculation as a means of contraception. We don’t like it in the medical community, either, for the simple reason that it’s not very dependable. Never mind that, unlike condoms, CI does not prevent the spread of sexually transmitted diseases (STDs), but we don’t very much like CI even compared with other non-barrier methods of contraception. The reason is similar to what your high school health teacher may have told you, namely that many people use the withdrawal method and still become pregnant, but the natural question from this is “what are the odds?”
Historically, this has been difficult to test, but a small survey-style study suggests that the withdrawal method –the way that it’s typically performed–, has a failure rate of 22 percent (22 percent of women using the method for contraception have an unintended pregnancy within 1 year). This is more than twice the failure rate of oral contraceptives (the pill) when taken not so perfectly (failure rate 9 percent), but 22 percent is horrible compared with oral contraceptives taken correctly (0.3 percent).
On the other hand, the 22 percent failure rate is only a little better than the failure rate of condoms used haphazardly (21 percent for the female condom; 18 percent with the male condom), whereas condoms used with perfect method entail a failure rate of 2 percent for the male condom and 5 percent for the female condom. These numbers kind of make coitus interruptus look like a bad idea, until you see that the study also shows that, when performed perfectly, CI results in a pregnancy rate of only 4 percent within a year. That’s not as good as oral contraceptives used perfectly, but surprisingly it’s in the same zone as perfect condom use, if your concern is preventing pregnancy, and if you’re not worried about STDs.
If you absolutely do not want to get pregnant, the numbers show that you should use either oral contraceptives and take them correctly, or use an intrauterine contraceptive, or have a sterilization procedure. But in terms of comparing most of the other methods, statistically, CI actually works to a certain extent, though with a big “IF” –if it is performed correctly. This raises the questions of what it means to perform CI “correctly” and what is the evidence that doing so has ever worked.
Here is the big caveat, one that you will hear from sex education teachers and obstetricians alike: pre-ejaculate –the liquid that drips out of the penis prior to ejaculation– contains viable sperm. It is not a myth, so you should take it seriously, before venturing to rely upon CI. The caveat to the caveat, however, is that analysis of pre-ejaculate samples has shown that only about one-third of men have a high enough number of viable sperm in their pre-ejaculate to get their partners pregnant. It’s kind of a hard thing to study in the laboratory, but probably this is the reason why coitus interruptus performed with perfect technique gives results comparable to condom use. Of course, your partner might be in the unlucky one-third, and then there is the reality that not all couples achieve perfect technique. Many screw up –forgive the pun.
Even so, performance of CI with technique ranging from perfect to utter failure means that it will work for a certain percentage of couples, over time. And so, if a society has a lot of people behaving in this way in their sexual lives, the fertility rate will go down. This is something that has happened in certain historical settings, most famously in 19th century France, when the birthrate dropped substantially, leading to a drop in population that affected the outcome of the Franco-Prussian war. One leading hypothesis for this turn of events is that the drop in French fertility was a direct result of CI gaining popularity in the years following the French Revolution. So while it may not work for you, the withdrawal method does work statistically, at the population level.
People knew about the coitus interruptus effect way back through ancient times, at least as far back to the writing of the biblical story of Tamar. She is a character who ends up as the ancestress of the people of Judah, of King David and the lineage of kings that religious Judaism posits will give rise to a Messiah figure, and finally, for Christians, of the lineage leading to Jesus. And all of this happens, because of coitus interruptus, through a storyline that’s impressively complex, given that it was written down more than 2,500 years ago.
Basically, what happens is that Tamar’s husband, Onan, pulls out of Tamar to avoid getting her pregnant. For doing this, the deity Yahweh punishes Onan with death, but Onan actually has a good reason for withdrawing; Tamar is not really his wife, but merely his levirate wife, his widowed sister-in-law. Prior to getting together with Onan, Tamar was married to Onan’s older brother Er, but the deity killed Er for being a bad guy. The biblical narrative doesn’t specify Er’s errors, but the medieval Jewish commentator Rashi wrote famously that Er must have been guilty of the same transgression as Onan. There’s not a shred of evidence in the text to support this conclusion, but, interestingly, some of the most fundamentalist Christian commentators in modern times have expressed interpretations identical to Rashi’s.
Whatever the reason for his brother’s death, Onan’s objection to fathering children through his sister-in-law is maybe not the same objection that you might have, were you to find yourself in a similar predicament. What bothers him instead is that, despite being the biological father of Tamar’s children, Onan would not be their legal father, nor would he be heir to the estate of his own father, Judah. Instead, he’d be a mere placeholder for his dead brother, Er. Now, seeing that his first two sons have suffered early deaths, Judah figures that his daughter-in-law is bad luck, so he holds off in allowing Shelah to marry Tamar. This leads Tamar to disguise herself as a common prostitute and stand by the road, where Judah takes her for a holy prostitute and unwittingly impregnates her with twins who end up carrying on his name.
Among Jews and Christians, the story of Tamar and Onan has been cited to justify various prohibitions against coitus interruptus, and, by extension, other birth control methods. In many cases, the rationale of such prohibitions has involved a belief that sex –and by extension semen– would be wasted, if utilized for anything other than procreation. The most famous adherent to this belief is the 12th century Jewish physician-philosopher Maimonides. Highly influenced by Aristotle of classical Greece, Maimonides typically responded to puzzling stories and rulings with explanations that sounded rational and in tune with natural law, based on what was known about nature in his time period. Unfortunately, however, both Maimonides and Aristotle lived in periods when human understanding of the natural world was rather scant.
Consequently, they both got a lot of things wrong. Regarding the matter of wasting semen, Maimonides believed that ejaculation drew energy from men, and that if experienced over and over, ejaculation would make a man age faster, get sick, smell bad, and die sooner. Today, however, we have data showing that frequent ejaculation actually can help protect a man against prostate cancer, a discovery that flies in the face of Maimonides’ idea. It seems that we have made some progress over more than 800 years, but this still doesn’t solve the problem of deciding what’s the best form of birth control. To do that, you need to begin by deciding what level of reliability you want.