Do victims of rape have biological defenses that prevent pregnancy?

Question

Pro life Rep. Todd Akin, who was running for Senate in Missouri, said:

“If it’s a legitimate rape, the female body has ways to try to shut that whole thing down.”

Needless to say, this claim is quite controversial. Is there any truth to it?

Answer 1

NO WAY!

There are a few sticky issues here that I will try to address.

First of all Mr. Akin is only talking about "legitimate rape" while not defining which rapes he considers legitimate. It could be the only rapes he considers legitimate are the ones where the victim doesn't get pregnant and if she does get pregnant, she must have been "asking for it," or maybe he feels she should have fought back harder. I don't know this is the exact case, but the use of "legitimate" is very telling, that he considering some specific cases of rape not legitimate. He could be using the word "legitimate" to exclude false accusations of rape, but by definition those are not cases of rape. I'm wondering what Mr. Akin wants to define legitimate rape as. Others continue to use their own definition of what a real legitimate rape entails:

Rape, ladies and gentlemen, is not today what rape was. Rape, when I was learning these things, was the violation of a chaste woman.⁽¹⁾ _{- Tennessee State Senator Douglas Henry}

Second of all, we do know rape victims get pregnant.

One study⁽²⁾ found that there the pregnancy rate of rape is 5% in women age 12-45, and 32,101 pregnancies result from rape each year in the United States. The conclusion of the study even reads:

Rape-related pregnancy occurs with significant frequency. It is a cause of many unwanted pregnancies and is closely linked with family and domestic violence. As we address the epidemic of unintended pregnancies in the United States, greater attention and effort should be aimed at preventing and identifying unwanted pregnancies that result from sexual victimization.

Even though there was a link between rape and violence, perhaps Mr. Akin doesn't consider those people surveyed to have experienced "legitimate rape." Perhaps he would consider what these women went through "legitimate":

During the conflict in the former Yugloslavia in the early 1990's, rape was used as a highly systematized instrument of war.

Women were kept in various detention centres where they had to live in intolerably unhygienic conditions, where they were mistreated in many ways including, for many of them, being raped repeatedly. Serb soldiers or policemen would come to these detention centres, select one or more women, take them out and rape them …. All this was done in full view, in complete knowledge and sometimes with the direct involvement of the local authorities, particularly the police forces. The head of Foča police forces, Dragan Gagović, was personally identified as one of the men who came to these detention centres to take women out and rape them.⁽³⁾

A Croatian Medical Journal study of 68 of these victims⁽⁴⁾ found that 29 got pregnant as a result of their sexual assault. That is 42.64% of them.

Forty-four of them were raped more than once, 21 were raped every day during their captivity, and 18 were forced to witness rapes. Most of the rapes (n = 65) were accompanied by physical torture.

I've established that rape victims, even in extreme cases, get pregnant. We come back to the question of: Is it less likely for sex as a result of rape to lead to a pregnancy? It is at least plausible that stress will in some way affect ovulation.

Catecholamines, prolactin, adrenal steroids, endorphins, and serotonin all affect ovulation and in turn are all affected by stress. ⁽⁵⁾

...

The biological interaction between stress and infertility is the result of the action of stress hormones at the brain level, especially on the hypothalamus-pituitary and on the female reproductive organs. Stress hormones such as catecholamines (adrenalin, nonadrenaline and dopamine) and the hypothalamic-pituitary-adrenal axis interact with hormones which are responsible for normal ovulatory cycles: i.e., gonadotropin releasing hormone (GnRH), prolactin, LH and FSH. Endogenous opiates and melatonin secretion are altered by stress and interfere with ovulation. ⁽⁶⁾

Stress can interfere with ovulation, but in practice, this doesn't prevent pregnancy in cases of rape. In fact, the study⁽⁷⁾ I found on the topic came to the conclusion that rape is more likely to produce a pregnancy than consensual sex.

Is a given instance of rape more likely to result in pregnancy than a given instance of consensual sex? This paper undertakes a review and critique of the literature on rape-pregnancy. Next, it presents our own estimation, from U.S. government data, of pregnancy rates for reproductive age victims of penile-vaginal rape. Using data on birth control usage from the Statistical Abstract of the United States, we then form an estimate of rape-pregnancy rates adjusted for the substantial number of women in our sample who would likely have been protected by oral contraception or an IUD. Our analysis suggests that per-incident rape-pregnancy rates exceed per-incident consensual pregnancy rates by a sizable margin, even before adjusting for the use of relevant forms of birth control.

So while technically Mr. Akin's comment might have some merit based on the abstract idea of stress affecting ovulation, based on the data, I can't call it at all correct. Raped women do get pregnant in large enough numbers, even moreso than women who have consensual sex. In addition, the claim is very dismissive and insulting to rape victims, particularly those who were impregnated. Not to mention it is just a tasteless thing to say.

References:

⁽¹⁾ Valenti, Jessica, writ. The Purity Myth: The Virginity Movement's War Against Women. 2011. Film.

⁽²⁾ Holmes, Melisa, Heidi Resnick, Dean Kilpatrick, and Connie Best. "Rape-related pregnancy: Estimates and descriptive characteristics from a national sample of women." American Journal of Obstetrics and Gynecology. 175.2 (1996): 320-325.

⁽³⁾ "ICTY: Kunarac, Kovač and Vuković judgement". United Nations International Criminal Tribunal for the former Yugoslavia. 2001-02-02.

⁽⁴⁾ Lončar, Mladen, Vesna Medved, Nikolina Jovanović, and Ljubomir Hotujac. "Psychological Consequences of Rape on Women in 1991-1995 War in Croatia and Bosnia and Herzegovina." Croatian Medical Journal. 47.1 (2006): 67-75.

⁽⁵⁾ Seibel, MM, and ML Taymor. "Emotional aspects of infertility." Fertility and Sterility. 37.3 (1982): 137-145.

⁽⁶⁾ Schenker, JG, D Meirow, and E Schenker. "Stress and human reproduction." European Journal of Obstetrics & Gynecology and Reproductive Biology. 45.1 (1992): 1-8.

⁽⁷⁾ Gottschall, Jonathan, and Tiffani Gottschall. "Are per-incident rape-pregnancy rates higher than per-incident consensual pregnancy rates?." Human Nature. 14.1 (2003): 1-20.

Answer 2

NO WAY anyone knows. Although their are biological reasons like those noted in other answers, reliable estimates are not available to make a determination one way or the other.

What was the Question?

Todd Akin's comments were taken out of context. Here is the full text of what Todd Akin said about rape, and the (video link).

Charles Jaco: Okay, so if an abortion can be considered in the case of, say, tubal pregnancy or something like that, what about in the case of rape? Should it be legal or not?

Todd Akin: Well, you know, people always want to try and make that as one of those things: "Well, how do you - how do you slice this particularly tough sort of ethical question?"

It seems to me, first of all, from what I understand from doctors, that's really rare. If it's a legitimate rape, the female body has ways to try to shut that whole thing down. But let's assume that maybe that didn't work or something.

You know, I think there should be some punishment, but the punishment ought to be on the rapist and not attacking the child.

Todd Akin's statement taken out of context seems ridiculous, because it is easy to find a single counter example of a woman who got pregnant from a rape. This isn't even close to what Todd Akin claimed. Todd Akin was arguing that you shouldn't use instances of rape to justify legalizing abortion, because pregnancy due to rape is really rare, he is not saying that pregnancy is never the result of rape. This is clarified in Todd Akin's apology video.

Say it ain't So?

Todd Akins is talking about false accusations when talking about "legitimate" rape. Todd Akins clarified his position on Aug 21, on the Mike Huckabee show (audio available).

You know, Dr. Willke has just released a statement and part of his letter, I think he just stated it very clearly. He said, of course Akin never used the word legitimate to refer to the rapist, but to false claims like those made in Roe v. Wade and I think that simplifies it….. There isn’t any legitimate rapist…. [I was] making the point that there were people who use false claims, like those that basically created Roe v. Wade.

Women do lie about rape. What percentage of rapes are false accusations? Once again, the numbers vary greatly. The US Department of Justice released a report Convicted by Juries, Exonerated by Science places the false accusation percentage between 20%-40% using DNA testing.

Every year since 1989, in about 25 percent of the sexual assault cases referred to the FBI where results could be obtained (primarily by State and local law enforcement), the primary suspect has been excluded by forensic DNA testing. Specifically, FBI officials report that out of roughly 10,000 sexual assault cases since 1989, about 2,000 tests have been inconclusive (usually insufficient high molecular weight DNA to do testing), about 2,000 tests have excluded the primary suspect, and about 6,000 have “matched” or included the primary suspect.

The fact that these percentages have remained constant for 7 years, and that the National Institute of Justice’s informal survey of private laboratories reveals a strikingly similar 26-percent exclusion rate, strongly suggests that postarrest and postconviction DNA exonerations are tied to some strong, underlying systemic problems that generate erroneous accusations and convictions.

(Note: FBI statistics do not differentiate between accusers who lie, make an honest mistake. Neither does it preclude that a rape didn't take place, only that the person accused was innocent.)

False accusations will clearly affect any estimates of legitimate rapes, which will in turn affect any study based upon unsubstantiated claims of rape by the "victim." Todd Akin clarified what he meant when he said "legitimate rape," but lets explore some other possible explanations for what is legally a rape, instead of resorting to believing that Todd Akin must have meant women who weren't asking for it, didn't fight hard enough, or were the victims of war crimes. These cases might not cause a biological response in the victim, because the aren't forcible rape.

• Statutory Rape
• Incapacitated Rape
• Drug/Alcohol Facilitated Rape

32,101? How confident are you?

Finally, we come to the heart of the matter. Is a woman less likely to become pregnant if forcibly raped, than with consensual sex.

How confident should we be that 32,101 pregnancies are the result of rape each year? I wasn't able to access the study online, but you can glean enough information from the abstract to see some problems with the estimate.

• STUDY DESIGN: A national probability sample of 4008 adult American women ...
• Among 34 cases of rape-related pregnancy, ...
• The national rape-related pregnancy rate is 5.0% per rape among victims of reproductive age ... and estimated 32,101 pregnancies

As I said, my local library didn't have online access to the study, so I can't verify their exact numbers or how they arrived at 5.0%. I was able to find secondary sources that explained some of the numbers from the study:

In their methods they called their study the National Women’s Study, and say that they interviewed 4008 women in the first wave. Each wave had fewer women. They said they noted 616 instances of rape from the 3031 respondents in wave three. How then, do they then say:

“Analysis of the National Women’s Survey raw data (without statistical weighting required for determining representative population estimates) indicates that there were 34 cases of rape-related pregnancy. A total of 30 women reported one rape-related pregnancy and two additional women reported two rape-related pregnancies. Of the 34 cases 21% occurred when the victim was aged 12 to 15 years, 27% occurred among women aged 16 and 17, and 52% occurred after age 18.”

This study is extrapolating estimates for the USA reproductive female (1996) (page 44): 67,047,000 women age (12-45), with only 616 rapes resulting in 34 pregnancies from a sample of 4008-3031 women. Using a handy dandy online Confidence Interval calculator (Confidence Level 95%, Sample Size: 616, Population: 3031, Percent: 5 = CI: 1.54). This represents a slightly greater than 30% margin of error. (Note: Hopefully I am using the right (someone correct me if I am wrong) sample size 616, not 34. Since I think the sample is 616 women with 5% (34 women) answering "Yes" to the quality of becoming pregnant as a result of the rape. If I was supposed to use 34, then the CI=7.29 which would make the margin of error greater than the estimated 5% pregnancy rate)

One of the authors of the study is Dean G. Kilpatrick, should know better (I'm just an amateur scientist). He should be more cautious when using figures that have a >30% margin of error. He is at least aware of other measures of rape, since he wrote a white paper Making Sense of Rape in America. One of the data sources used to measure rape listed on page 3 is National Violence Against Women Survey (NVAWS), which has a nice little chart (page 7) showing estimated standard error. The NVAWS also notes:

Estimates with RSEs [Ratio Standard Error] that exceed 30 percent were deemed unstable and were not tested for statistically significant differences between or among groups. These estimates have been identified in the tables and should be viewed with caution.

I guess Kilpatrick wasn't cautious, since he uses a similar figure in the white paper (rape was 0.27%) that the NVAWS cautions about (page 14, Exhibit 14 & 15):

Because annual rape victimization estimates are based on responses from only 24 women and 8 men who reported having been raped, they should be viewed with caution.

Update: I have included another secondary reference for the Johnathan Gottschall estimate provided in the accepted answer (Reference 7), that challenges the 6.4% rape pregnancy rate claimed in that study.

The Gottschalls’ article looked at the National Violence Against Women survey, which polled 8,000 women. Of the 405 rape victims in the poll who fit the studies’ methodology, about 6.4 percent of them became pregnant. The Gottschalls think the best studies show consensual sex resulting in pregnancies about 3 percent of the time. Why the gap?

Using data from the (National Violence Against Women Survey) own Relative Standard Error chart, you will note that this gives an RSE of >30%, which means that Gottshall ignored the NVAWS recommendations about making statistical comparisons regarding subsets with such high RSE. In the politico article (linked above as the Update: secondary ref), Jonathan Gottschall even admits:

But Gottschall did warn that methodological problems mean the numbers “aren’t carved in a stone.”

From the major studies listed in Kilpatrik's whitepaper (see each national studies overview and methodological limitations), their doesn't exist a reliable estimate the chances of pregnancies from rape, and without a reliable rape pregnancy rate, a comparison cannot be made to consensual sex leading to pregnancy. Not only that, but the studies (and consensual sex) estimates usually cannot account for confounding factors that might affect the outcome. The Rape Abuse and Incest National Network does a good job of breaking these down.

Conclusions

When taken in context, it is clear that legal abortions for rape victims are very rare (Atkins actual claim). Without reliable estimates for the number of rapes, or resultant pregnancies from rape, it is impossible to tell if a woman is less likely to get pregnant after being raped than having consensual sex (the [possible] claim that Atkins says he gets from doctors).