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In time his idea began to win converts. Janet Rich-Edwards, an epidemiologist at Brigham and Women's Hospital in Boston, deliberately set out to disprove the Barker hypothesis. "I was convinced that your current risk factors determine your odds of developing disease," says Rich-Edwards, "not something that happened when you were a fetus." But, she adds, "there's nothing like your own data to change your mind." Rich-Edwards analyzed findings from the Nurses' Health Study, a long-running investigation of more than 120,000 RNs. Even when she took account of the nurses' adult lifestyles and socioeconomic status, the relationship between low birth weight and cardiovascular-disease risk remained robust. "Similar studies have been conducted at least two dozen times since then," she notes. "It's one of the most solidly replicated findings in the field of public health."
As a journalist who covers science, I was intrigued when I first heard about fetal origins. But two years ago, when I began to delve more deeply into the field, I had a more personal motivation: I was newly pregnant. If it was true that my actions over the next nine months would affect my offspring for the rest of his life, I needed to know more.
Of course, no woman who is pregnant today can escape hearing the message that what she does affects her fetus. She hears it at doctor's appointments, sees it in the morning newspaper and in the pregnancy guidebooks: Do eat this, don't drink that, always be vigilant but never stressed. Expectant mothers could be forgiven for feeling that pregnancy is nothing but a nine-month slog, full of guilt and devoid of pleasure, and this research threatened to add to the burden.
But as I began applying what I learned to my own pregnancy, I developed a very different perspective on fetal origins. The scientists I met weren't full of dire warnings but of the excitement of discovery and the hope that their discoveries would make a positive difference. We're used to hearing about all the things that can go wrong during pregnancy, but as these researchers are finding out, it's frequently the intrauterine environment that makes things go right in later life.
The Power to Change Behavior
Take, for example, the prospect of maintaining a healthy weight. Americans are heavier than ever, and their weight gain begins ever earlier in life. Could it be that a tendency for obesity is being programmed in the womb? A pair of studies conducted by researchers at Harvard Medical School suggest that may be the case: the greater a woman's weight gain during pregnancy, one study found, the higher the risk that her child would be overweight by age 3. The second study indicated that this relationship persists into the offspring's adolescence. Compared with the teenagers of women who had moderate weight gain during pregnancy, those of women who had excessive weight gain were more likely to be obese.
Of course, children could share eating habits or a genetic predisposition to obesity with their mothers; how can we know the prenatal environment is to blame? Researchers have compared children born to obese mothers with their siblings born after the mothers have had successful antiobesity surgery. The later-born children inherited similar genes as their older siblings, and (research shows) practice similar eating habits, but they experienced different intrauterine environments. In a 2006 study published in the journal Pediatrics, researchers found that the children gestated by women postsurgery were 52% less likely to be obese than siblings born to the same mother when she was still heavy. A second study by the same group, published in 2009, found that children born after their mothers lost weight had lower birth weights and were three times less likely to become severely obese than their older brothers and sisters.
"The bodies of the children who were conceived after their mothers had weight-loss surgery process fats and carbohydrates in a healthier way than do the bodies of their brothers and sisters who were conceived at a time when their mothers were still overweight," says John Kral, a professor of surgery and medicine at SUNY Downstate Medical Center in New York and a co-author of both papers. Their metabolisms were, in effect, made normal by their prenatal experience perhaps through a process known as epigenetic modification, in which environmental influences affect the behavior of genes without altering DNA. It may be that the intrauterine environment is even more important than genes or shared eating habits in passing on a propensity for obesity, Kral says. If that's so, helping women maintain a healthy weight before and during pregnancy may be the best hope for stopping obesity before it starts.
The science of fetal origins also offers hope to people who believe that heredity has doomed their families to disease people like the Pima Indians of the Gila River Reservation in Arizona, who have the highest rate of Type 2 diabetes in the world. There is little doubt that the high incidence of diabetes among the Pimas, and among Native Americans in general, has a significant genetic component. But new research from a study that has followed a large group of Pima Indians since 1965 points to an additional influence: prenatal experience. During pregnancy, a diabetic woman's high blood sugar appears to disrupt the developing metabolism of the fetus, predisposing it to diabetes and obesity.