Lessons From the Womb
Your thoughtful message anticipates much of what I have to say about the state of fetal origins research. Science is indeed discovering more and more about what you call "the profound entwining of mother and child" during pregnancy. You mention your reporting on the contribution of maternal cells to the fetal body; I find myself thinking also of your recent Slate story about the failure (so far) to invent an artificial womb capable of gestating a human fetus. The reason for that failure, you explain, is that the intrauterine environment is so "complex and crucial," with "mother and fetus even more deeply enmeshed than scientists used to think." At the very beginning of our lives, you write, "we apparently need mothers even more than we ever thought."
In the three decades of its existence, the science of fetal origins has made significant discoveries; at the same time, its rapidly expanding body of research is indeed variable in quality. There are small, preliminary studies like the one on exercise you cite along with large, sophisticated studies published in leading journals. A 2007 study of almost 12,000 women, for example, conducted by researchers from the National Institutes of Heath and appearing in the Lancet, suggested that women who eat less than 12 ounces of seafood a week during pregnancy have children with an increased risk of low verbal IQ, social and communication problems, and poor fine-motor skills at 6 months to 8 years of age. A 2007 study of 1,044 mother-child pairs, led by researchers at Harvard University and published in the American Journal of Obstetrics and Gynecology, reported that women who gained more weight during pregnancy—even within the recommended range of 25 to 35 pounds for a normal-weight woman—had children who were heavier at the age of 3.
In what will be the biggest research effort of its kind, the National Children's Study—conducted by a consortium of federal agencies and just getting under way this year—will enroll 100,000 pregnant women from across the country. Experimenters will interview the women about their habits and behaviors during pregnancy, sample their hair, blood, saliva, and urine, and test the water and dust in their homes. The women's offspring will be tracked from before they are born to the time they turn 21. The first results are expected in 2012. The design of the National Children's Study is itself evidence of the ascendancy of fetal origins: From now on, any comprehensive examination of early influences on later health will have to include the months before birth.
We're going to be hearing a lot about this research, and we desperately need a better way to understand it. You say that these studies have often been the object of "hype"; I think we can be more specific and take note of the particular frame that is almost invariably placed around the findings. That frame looks something like this: Because of her negligence or selfishness, a pregnant woman is constantly in danger of harming her fetus. Society has little stake in her well-being or responsibility for her welfare. Pregnant women are on the hook should anything go wrong.
My book, Origins, is an effort to offer an alternative understanding—a perspective that is both more generous and humane and more accurate and realistic. The pregnant woman is neither a passive incubator nor a source of ever-present danger to her fetus but a powerful and often positive influence on her child even before it's born. Society has a large and long-term stake in the health of pregnant women and fetuses. And pregnancy is not a nine-month wait for the big event of birth but a crucial period unto itself—"a staging period for well-being and disease in later life," as one researcher puts it.
It is true that this new way of thinking about pregnancy can take some getting used to. You express incredulity, for example, at the notion that natural selection goes on in the womb. But this idea is hardly on the "fringe." More than 20 years ago, the Yale University biologist Stephen Stearns noted that some organisms—from wheat plants to fruit flies to chickens—produce many more fertilized zygotes than are actually born, hatched, or released. Stearns proposed that the bodies of the mothers in some species were overproducing zygotes, identifying those with lower expected fitness, and allowing some to perish in order to invest in more promising offspring. Over the past few centuries, as infant and child mortality rates plunged and as adults lived longer and longer, the womb became the primary arena for natural selection.
For humans too, only an estimated 20 percent to 40 percent of fertilized eggs actually result in a live birth. UC-Berkeley professor Ralph Catalano has applied this theory to a number of human populations with intriguing, if not yet conclusive, results. Catalano hypothesizes that weak fetuses, more often males, may be "culled" in anticipation of a stressful environment. This idea is not necessarily in tension, as you suggest, with David Barker's that fetuses adjust their energy needs based on cues from the environment in utero. In fact, these adjustments may well be part of the same process of fitting the fetus to the particular world on the other side of its womb. These ideas surprise and provoke because we're not accustomed to thinking of the intrauterine environment as a theater of action, a setting where consequential events take place.
Just how consequential, compared to factors like genes and environment? It's honestly impossible to say, because these various strands can't be unbraided. Although we receive our complement of DNA at conception, the way those genes are expressed continues to be modified—a process that happens with special frequency in utero. And we can't talk about the impact of the "environment" without considering our first environment, the womb, where the fetus is already being shaped by his mother and her world.
But if prenatal influences are hopelessly bound up with both nurture and nature, the bounded timeline of pregnancy makes it into an ideal opportunity for intervention. It's a discrete period of nine months during which women are especially open to making changes in their habits and behaviors, and during which they are in regular touch with doctors or nurses. What's more, investments in this period can be more cost-effective than investments made later on. After all, what makes more sense: controlling a pregnant woman's diabetes for nine months (which effectively eliminates the doubling of obesity risk her offspring would experience if she remained untreated, according to this study)—or waiting to treat her son until he's 50 years old and has full-blown diabetes that requires weekly dialysis? From both an economic and a moral standpoint, starting early seems the right thing to do. And we need not face a forced choice between helping pregnant women and fetuses and helping young children, as your question implies. Research shows that enrolling women while they are pregnant is the best way to keep mothers and children through an intervention program (like the Nurse-Family Partnership, memorably described by Katherine Boo in The New Yorker as the "swamp nurse" program).
But we have largely ignored these opportunities in favor of heaping guilt and anxiety on individual pregnant women. In writing Origins, I did deliberately look for positive steps that women can take during pregnancy, hoping to provide an antidote to the poisonous emotional climate in which many of us find ourselves. You ask whether there is a risk to overstating the promise of fetal origins. Yes, of course—and I've tried my level best to avoid overstatement. But there is a risk, too, in dismissing research that could be changing minds and improving health right now. We should proceed with caution, yes. But the science of fetal origins is moving forward. And that's for the good.
Annie Murphy Paul is the author of Origins: How the Nine Months Before Birth Shape the Rest of Our Lives and the forthcoming Brilliant: The Science of How We Get Smarter.