ast week Missouri Representative Todd Akin made an unusual statement during
his Senate race:
"First of all, from what I understand from doctors, (pregnancy from rape) is really rare. If it's a legitimate rape, the female body has ways to try to shut that whole thing down."
This statement has created a firestorm of controversy. It's very unusual for a politician to expound an unproven medical hypothesis, and doing so seems to be regarded by many Republicans and Democrats as a potentially fatal political gaffe. John F. Di Leo, a recovering politician himself, explains the political issues very well.
In fact, Akin's comment sounded pretty tame to me. It's fairly obvious that what Akin was trying to say was that in cases of actual, forcible rape (as opposed to cases of non-rape), the body may have some protective mechanism to prevent pregnancy. But is that really true? What are the scientific facts?
Scientists have discovered many ways by which stress influences pregnancy. Human biology is more complicated than we know. We are programmed, physically and mentally, to respond to environmental and social stimuli in many ways that we're only now beginning to understand. So it would be just as foolish to dismiss or ridicule Akin's hypothesis, or to call the idea "medieval" or "ignorant," as some commentators have done, as it would be to accept it without understanding the facts.
Stress and population growth
A good example of how nature's wisdom works is the way the birth rate adapts to social conditions. It is well known that as population density increases, the birth rate declines [17]. It used to be that this was attributed to competition for resources: when there are too many people, there's not enough food, so the babies starve. Et voilà, the rate of population growth goes down. In recent years, it has become clear that the relationship also holds in wealthy countries where there's more than enough food to go around. Something in the human brain we don't understand can affect whether a woman gets pregnant. Whether it's stress or some other factor remains to be discovered.
Biological effects of stress on pregnancy
Victims of forcible rape often experience severe, long-term stress, as well as anxiety and depression. How do these factors affect their ability to conceive?
Many studies have shown that stress and anxiety correlate with lower conception rates. Stress increases corticotrophin-releasing hormone (CRH), adrenocorticotrophic hormone (ACTH), and glucocorticoids. High levels of these hormones can inhibit conception by interfering with the timing of ovulation and shortening the luteal phase [1]. Stress also increases the levels of proinflammatory cytokines, which can cause complications of pregnancy, including preeclampsia and premature rupture of membranes [2].
Minor stress seems to have little effect. In 2003 Boivin [16] concluded that the evidence and the quality of the studies on minor stress done so far were insufficient to draw a definitive conclusion. Lynch et al. [4] compared pregnancy rates with self-reported levels of psychosocial stress, anxiety, and depression in 339 women between 18 and 40 years of age. After smoking, caffeine use, and frequency of intercourse were eliminated, there was no detectable correlation between ordinary, everyday stress and fecundity.
However, other researchers have found that depression and job stress increase the failure of in vitro fertilization [5]. A study done by the U.S. National Institutes of Health found that salivary α-amylase, which is an indicator of sympathetic nervous system activation (in other words, acute stress), significantly reduced the probability of becoming pregnant after correction for alcohol consumption, age, and intercourse frequency [6]. However, salivary cortisol (chronic stress) did not correlate with fecundity.
These mixed results with mild, day-to-day stress are confounded by the interactions
between anxiety, personality type, and physical health. The much higher levels of
stress produced by rape might be expected to have a stronger effect. Unfortunately,
the scientific literature here is crammed with politically biased articles influenced
The stress hormone cortisol. Brown=carbon, Red=oxygen, White=hydrogen.
Only three hydrogens are shown. Cortisol has a four-ring structure
similar to cholesterol, from which it is synthesized in the adrenal cortex.
by women's rights issues and the abortion debate. One example is an article by Stotland
[7] whose main point is that there are many methodological difficulties in studying it,
and the pro-life people should basically go away. The research on post-traumatic stress
is mainly focused on childbirth, rather than rape, as a traumatic event.
The harmful effects of stress during pregnancy are well documented. Stress during pregnancy can result in reduced birth weight and serious neurological impairment [8,9]. Psychosocial stress can increase behavior that is detrimental to pregnancy, including smoking and substance abuse. The detrimental effects of stress on sexual functioning are also well understood [3]. However, the effects of acute, traumatic stress on conception in humans have been inadequately studied.
Animal studies
In farm animals, the answer is clear: chronic stress impairs female reproduction capacity, and acute stress, if it occurs at a critical time, can impair reproduction [10,14]. In pigs, stress reduces implantation and impairs embryo development [12].
The effects of chronic stress are mediated through cortisol, while acute stress acts by activating the hypothalamo-pituitary-adrenal system, causing a release of corticotrophin releasing hormone (CRH) and vasopressin from the hypothalamus [11]. CRH in turn stimulates the pituitary gland to release ACTH, β-endorphin, and other molecules called proopiomelanocortin-derived peptides. ACTH releases cortisol, progesterone, and other powerful hormones from the adrenal cortex. Acute stress also activates the sympathetic nervous system, causing adrenaline and noradrenaline to be released.
In layman's terms, this means that acute stress causes the release of adrenaline and stress hormones which raise your blood pressure, increase your blood glucose levels, and reduce healing. In individuals genetically predisposed to stress, this can produce a transient impairment of fertility. Although most of these studies were done in pigs, the conclusions probably apply to humans as well.
In rats, stress on the morning of proestrus causes a reduction in the number of oocytes [13]. Stress reduces the amounts of luteinizing hormone, progesterone, and prolactin. Angiotensin II, a blood pressure-regulating hormone which promotes the release of other hormones from the adrenal cortex, is partly responsible for these effects.
So we can conclude that in animals, stress really can "shut that whole thing down," at least some of the time. But what about humans? The question is not whether pregnancy can result from rape—that is certainly true. The question is: can severe stress resulting from violent rape [see ref. 18] interfere with conception? It's not unreasonable to think it might, sometimes, but a lot more research is needed [15] before we can say for sure.
It is tragic that there is more interest in fertility rates in farm animals than in humans. It seems that in our society, the current focus is on issues such as homosexuality and abortion, whose goal is to reduce fertility than increase it. We are still living in the post-birth-control-pill era. A large constituency still thinks of abortion as part of their lifestyle, and derive an economic benefit from it. That would have to change before the ethical issues of abortion can be addressed. But regardless of one's opinion on abortion, we should be grateful to Todd Akin, if not for putting his foot in his mouth, at least for reinvigorating the discussion.
References
[1] Nakamura, K., Sheps, S., Arck, P. (2008). Stress and reproductive failure: Past
notions, present insights and future directions. Journal of Assisted Reproduction
and Genetics, 25, 47-62.
[2] Coussons-Read, ME, Okun, ML, Nettles, CD (2007). Psychosocial stress
increases inflammatory markers and alters cytokine production across pregnancy.
Brain Behavior and Immunity, 21, 343-350.
[3] Anderheim L, Holter H, Bergh C, Moller A (2005). Does psychological stress
affect the outcome of in vitro fertilization? Human Reproduction, 20, 2969-2975.
[4] Lynch CD, Sundaram R, Buck Louis GM, Lum KJ, Pyper C. (2012).
Are increased levels of self-reported psychosocial stress, anxiety, and depression
associated with fecundity? Fertil Steril. Aug;98(2),453-8. Epub 2012 Jun 13.
[5] Cwikel J, Gidron Y, Sheiner E (2004). Psychological interactions with
infertility among women. European Journal of Obstetrics & Gynecology and Reproductive
Biology, 117, 126-131.
[6] Louis GM, Lum KJ, Sundaram R, Chen Z, Kim S, Lynch CD, Schisterman EF, Pyper C.
(2011). Stress reduces conception probabilities across the fertile window: evidence
in support of relaxation. Fertil Steril. Jun;95(7), 2184-9. Epub 2010 Aug 5.
[7] Stotland NL. (1997). Psychosocial aspects of induced abortion.
Clin Obstet Gynecol. Sep;40(3):673-86.
[8] Hirst JJ, Walker DW, Yawno T, Palliser HK. (2009).
Stress in pregnancy: a role for neuroactive steroids in protecting the fetal and
neonatal brain. Dev Neurosci. 31(5),363-77. Epub 2009 Aug 15.
[9] Hobel CJ, Goldstein A, Barrett ES. (2008).
Psychosocial stress and pregnancy outcome.
Clin Obstet Gynecol. Jun;51(2), 333-48.
[10] Turner AI, Tilbrook AJ. (2006).
Stress, cortisol and reproduction in female pigs.
Soc Reprod Fertil Suppl. 62,191-203.
[11] Buckingham JC, Cowell A-M, Gillies GE, Herbison AE, Steel JH (1997).
The neuroendocrine system: anatomy, physiology and responses
to stress. In Stress, stress hormones and the immune system Edited by:
Buckingham JC, Gillies GE, Cowell A-M. John Wiley & Sons, Ltd,
Chichester; 9-47.
[12] Edwards RL, Omtvedt IT, Turman EJ, Stephens DF, Mahoney GWA (1968).
Reproductive performance of gilts following heat stress
prior to breeding and in early gestation. J Reprod Fertil.
52(Suppl), 47-61.
[13] Donadio MV, Kunrath A, Corezola KL, Franci CR, Anselmo-Franci JA,
Lucion AB, Sanvitto GL. (2007).
Effects of acute stress on the day of proestrus on sexual behavior and ovulation
in female rats: participation of the angiotensinergic system.
Physiol Behav. Nov 23;92(4):591-600. Epub 2007 May 22.
[14] Einarsson S, Brandt Y, Lundeheim N, Madej A. (2008).
Stress and its influence on reproduction in pigs: a review.
Acta Vet Scand. Dec 10;50,48.
[15] There, I said it!
[16] Boivin J. (2003). A review of psychosocial interventions
in infertility. Soc Sci Med. Dec;57(12):2325-41.
[17] This has been observed in many species, including humans. Some models predict
this to be true only at densities near or above the ecosystem's carrying capacity.
At very low densities, extinction predominates.
Fowler, C.W. (1981). Density dependence as related to life
history strategy. Ecology 63 (3), 602-610.
Firebaugh G. (1982). Population density and fertility in 22
Indian villages. Demography.Nov;19(4):481-94
Lutz, W., Testa, M., Penn, D. (2007). Population Density is a Key
Factor in Declining Human Fertility. Population and Environment 28 (2),
69-81
[18] The Democrats' position is just as confusing as Akin's, with Obama saying
that "rape is rape" and Whoopi Goldberg saying that some rape is not "rape-rape,"
for instance when it is committed by a famous film producer.
If some rape rape is not rape-rape rape, then all rape rape must be rape rape-rape.
On the other hand, if rape-rape rape is different from rape rape, then rape-rape
rape-rape must also be different from rape rape-rape. Otherwise, the terminology
would be just confusing.