Context and Variation

Context and Variation

Human behavior, evolutionary medicine… and ladybusiness.

Here is Some Legitimate Science on Pregnancy and Rape


Trigger warning: discussion of violence against women and graphic mention of miscarriage.


So Congressperson Todd Akin of Missouri has said some interesting things. Referring to the possibility of pregnancy after rape, and whether abortion should be allowed in this circumstance, he said according to his understanding “if it’s a legitimate rape, the female body has ways to try to shut that whole thing down,” but that, should one embryo slip through, that “the punishment should be on the rapist, and not attacking the child.” In Akin’s non-apology about his insensitivity towards the “thousands” of rape survivors each year, he remains firm on the point that abortion shouldn't be allowable for pregnant victims, saying “…I believe deeply in the protection of all life and I do not believe that harming another innocent victim is the right course of action.”

I don’t like writing about rape. I didn’t like turning my Laser Beam Eyes of Ladybusiness Justice on my Twitter feed today, which was a constant stream of information, reaction to, and anger about Akin and his baseless, stupid comments. Rape reminds me of the ways in which I am powerless, simply by being female. It doesn’t matter how many contact sports I play or muscles I build. It doesn’t matter how big my husband is. Sometimes I look at my life, and see what I’ve built, and how I’ve tried to protect myself. And I wonder what measures other women have taken for the same reasons, measures that ultimately mean little in the face of cultural conditioning to make men happy, of sexual dimorphism in musculature, of a powerful rape culture.

Some legitimate context

Unfortunately, it is rather normal to be a survivor of sexual assault if you are female. One out of six women in the United States have been the victim of rape or attempted rape, and that is using a rather tight definition that does not include many kinds of assault victims can experience. 64,080 women were raped in the US between 2004-2005. Sixty four thousand and eighty. That’s tens of thousands, not just thousands. In one sample of college-aged men, one in sixteen men admitted to raping women they either knew were too intoxicated to give consent, or they used physical force. Among these men who readily admitted to rape but had never been arrested or convicted, they committed an average of six rapes each and proudly described their sexual exploits to the interviewer (Lisak and Miller 2002).

Think of all the illnesses and conditions that make the news regularly. Take gluten intolerance, for example. The incidence for gluten intolerance is somewhere around 1% (more or less, depending on how you define it). Think on how many people you know are gluten intolerant. You know at least one, don’t you?

Now think of the women who have been raped compared to this number – about 17%. There are so many more of us out there who have been affected by sexual assault, unwanted sexual touching, sexual violence, rape and abuse that the number is likely greater than this. And though I display my gluten intolerance every time I ask an annoying, pointed question about a menu item at a restaurant, other ways I and other women identify are not exactly the subject of normal conversation.

And so, you know survivors of sexual assault. You know many of them, in fact, an astounding, upsetting number of them. It is not only normal to know multiple sexual assault survivors, it is normal in our culture for women to be afraid of rape and on the defensive around men for gigantic portions of their lives. And so, even for women who have never and will never be raped, it is a fear-inducing, triggering reminder that our safety is never fully in our own hands.

So let’s turn our attention to some goddamn science.

Allow me to amaze and dazzle you with a very basic reading of a rather clear-cut and unambiguous literature, something Akin could have done even without my fancy PhD. Especially since he is on the Committee on Science, Space, and Technology.

The frequency of legitimate conception

How frequently do raped women get pregnant? It would seem from Akin’s comment that this is a very rare occurrence. However, current evidence suggests it is the same as the pregnancy rate for a single act of intercourse. Ergo, pregnancy from rape occurs as frequently as pregnancy from consensual sex.

A lot of people are citing the Holmes et al (1996) paper that found a 5% pregnancy rate among rape survivors from 12 to 45 years of age. This is a great study that performed several telephone interviews with 4008 participants over three years to determine rates of rape (413 individuals experienced 616 completed rapes, a lifetime incidence of over 13% in this sample) and rates of pregnancy from rape (20 were reported from 19 individuals, or 5%).

In a separate study, Wilcox et al (2001) draw from their amazing prospective dataset from the 1980s where they asked women who were trying to conceive to collect urine every day. They were able to detect hormones, and thus pregnancies and fetal losses, because of these daily urine collections. Work on this dataset from Wilcox, Baird, and others represents the gold standard for our understanding of early pregnancy, fetal loss, and the timing of implantation in the luteal phase of the menstrual cycle. In this paper, the authors are able to show what the possible pregnancy rates are for a given day in the menstrual cycle, taking into account the normal variation many women experience in the length of their cycle and timing of ovulation:

Figure from Wilcox et al 2001 showing chance for pregnancy through the menstrual cycle in women with "normal" and "irregular" cycles.

What they find is that the rate of pregnancy on any given day is about 3.1%, a little lower than the Holmes et al estimate. What Wilcox et al also does well is demonstrate first how the vulnerability to get pregnant varies across the cycle, but also how it is most certainly not zero at the times many of us assume we are not fertile. I’m not sure I am convinced the difference in the rates in these two studies is meaningful, and instead I suspect it is just a result of natural variation based on participant sample. Wilcox et al themselves suggest that the higher number for Holmes et al is a result of methodological differences. But only more studies will help us settle this.

So, rape and consensual sex have the same pregnancy rate. This means that of those 64,080 US rapes in 2004-2005, minus the 15% of rapes that are of children under the age of 12 which gets us to 54,468 rapes of almost all reproductively-aged women, somewhere between 1,689 (3.1%) to 2,723 (5%) pregnancies from rape could have occurred in that year alone. Somewhere around half of those women were probably using some form of hormonal contraception, so let’s hope the numbers are even lower. Unfortunately, access to emergency contraception is still a challenge for rape survivors who go to hospitals, particularly Catholic hospitals, to receive treatment (Smugar et al. 2000).

Legitimate stressors

It’s almost not worth discussing any mechanism that Akin may have dreamed up that allows women to “shut down” a potential conception from rape, now that we see the rates are the same. Except that some people are still trying.

Lest my own words come back to bite me, since I have seen this idea floating through the interwebs I want to address it now: yes, psychosocial stress is associated with fetal loss in some samples. That is not the same thing as saying that stress causes fetal loss. Some women are more reactive to stress than others, and this seems to be based on genes and early childhood experiences. As I pointed out in my post, it certainly isn't something women have conscious control over. And so it is irrational to link the stress of rape, while awful and severe, to fetal loss, when we understand the mechanism of the stress response and its relationship to pregnancy so poorly, and when we know next to nothing regarding how variation in stress reactivity is produced.

A legitimate word on preeclampsia

And then the always-brilliant Jeremy Yoder and Scicurious pointed me to an older post of Jesse Bering’s that he retweeted today in response to the Akin mess. The gist of the blog post’s argument is that preeclampsia is a mechanism to protect women from unwanted babies with men they don’t know – such as rapists. Bering and others justify this claim with evidence that preeclampsia is more common in women who have not had long-term sexual relationships with the genetic father of the child (as in one night stands, shorter relationships, sperm donors). And that part of it – this correlation between low exposure to the genetic father’s semen and preeclampsia – is indeed born out in the literature.


Preeclampsia is also more common in first pregnancies, with multiples, in obese women and in women over thirty five. And sometimes you get it just because you have shitty luck. In fact, preeclampsia is more common in any of those conditions than it is in women without those risk factors but with shorter sexual relationships with the genetic father. Preeclampsia is a condition where implantation is not deep enough, possibly because the mother has some kind of immune reaction to the fetus. This makes sense with all of the risk factors described above, because all of them stimulate some sort of inflammatory response, which could disrupt implantation (Clancy 2012).

Here’s the other problem. Preeclampsia is not early miscarriage, the only scenario I could imagine where this would become an adaptive mechanism. It is a condition that can lead to very late term miscarriage or stillbirth, not to mention maternal death. The only treatment for preeclampsia, in fact, is to deliver the baby. In industrialized populations this can be done fairly easily, provided the preeclampsia isn’t too severe or the pregnancy is far along before symptoms develop. Under ancestral conditions, women would either have a messy, horrible, late term miscarriage where the baby would die, or if they’re extra unlucky their placenta would abrupt and they too would bleed out and die.

I struggle to see anything adaptive in this. I struggle to see any benefit that could outweigh this cost.

Finally, most perpetrators today are men the victims know. Many, many rapes are part of a broader suite of intimate partner violence behaviors. The idea that preeclampsia could somehow be a pregnancy avoidance mechanism assumes that the rapist is not the woman’s partner, has not in fact had sex, consensual or not, with her for a number of years. It seems likely to me that the kinds of rape we have today are similar to the kinds of rape we had in the ancestral period.

The science behind all of this is straightforward. Akin could have had some assistant or intern look it up in minutes via Google Scholar or PubMed, as a few paper abstracts would have been more illuminating than whatever he was reading. But Akin wasn’t interested in the science, he was interested in how well he could use fear and false information to control women.

In all that powerlessness, that is one thing women have to fight back. When women have the right information they do not have to withstand the claim that they can’t get pregnant from rape, or it must not have been that stressful if they are pregnant. Women and their children who have survived preeclampsia do not have to endure another man telling them that it is a mechanism to avoid rape, or that they could reduce their chances of preeclampsia next time if they’d only swallow. A clear picture of reality dispels the gloom of sexism better than any cleverly worded blog post ever could.


Clancy KB. 2012. Inflammation, reproduction, and the Goldilocks Principle. In: Clancy KB, Hinde K, and Rutherford JR, editors. Building Babies: Primate Development in Proximate and Ultimate Perspective. New York: Springer.

Holmes MM, Resnick HS, Kilpatrick DG, and Best CL. 1996. Rape-related pregnancy: Estimates and descriptive characteristics from a national sample of women. American Journal of Obstetrics and Gynecology 175(2):320-325.

Lisak D, and Miller P. 2002. Repeat rape and multiple offending among undetected rapists. Violence and Victims 17(1):73-84.

Smugar S, Spina B, and Merz J. 2000. Informed consent for emergency contraception: variability in hospital care of rape victims. Am J Public Health 90:1372-1376.

Wilcox AJ, Dunson DB, Weinberg CR, Trussell J, and Baird DD. 2001. Likelihood of conception with a single act of intercourse: providing benchmark rates for assessment of post-coital contraceptives. Contraception 63(4):211-215.

(Edited at 7:35am CST to correct error -- Akin is a Congressperson, not Senator.)

The views expressed are those of the author and are not necessarily those of Scientific American.

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