Kate Clancy is one of my favorite bloggers. An anthropology professor at the University of Illinois, she studies the evolution of female reproductive anatomy. Her blog covers science I don't see anywhere else—the human evolution, cultural anthropology, and behavioral science behind ladybusiness.
So Clancy's blog was one of the first places I looked yesterday after reading about Missouri Rep. Todd Akin thoughtful commentary on female biology. In a long, well-written, and (fair warning) rather graphic post, Clancy talks about what we know about rape—think of it this way, you know way more people who have been raped than who have a gluten intolerance—and the way that emotional trauma affects conception and pregnancy.
First off, there is absolutely no difference in the rate of conception between women who have been raped and those who had consensual sex. Clancy breaks this down nicely in her blog post, and even offers a surprising tidbit from the research literature that all people should consider—at any given day in a woman's cycle (even days when she is supposedly "infertile") there's about a 3% chance of unprotected sex leading to a pregnancy.
The impact of stress on miscarriage is a lot messier. I've mentioned here before that we know very, very little about miscarriage, relative to a lot of other medical issues. To paraphrase my family practice doc, when you start talking about conception and miscarriage you very quickly wander past the small amount of hard evidence and straight into voodoo. And also into the counter-intuitive nature of reality. For instance, from reading Jon Cohen's excellent book on miscarriage science, Coming to Term, I know that one of the very few miscarriage interventions that's ever performed better than placebo in multiple trials is something called "Tender Loving Care". The idea: For whatever reason, women who have had recurrent miscarriages have a greater chance of carrying the next pregnancy to term if they have regular access to mental health services, stress-relieving practices like meditation, and doctors who listen and respond to their fears. But that's not the same thing as saying that stress, or a scare, or a severe mental trauma will, inevitably, cause a miscarriage. Here's Kate Clancy:
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.
Basically, while stress (and the associated hormones) are correlated with a higher risk of miscarriage in some (but not all) studies, that seems to have more to do with an individual's biological makeup than it does with the source of the stress. And, frankly, we barely know enough to even say that.
• Read Jon Cohen's book, Coming to Term. (I keep recommending this, but, seriously, it's wonderful. And a hugely sane-making force in my life.)
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.