First Acts

I prided myself on being low-key about my pregnancy. I didn't read What to Expect When You're Expecting—OK, so I bought a copy, but I only used it as a reference. I traveled, I socialized, and I worked full-time until five days before giving birth, even though I was carrying twins. I did not want to believe that anything essential about me had changed. That is, until the night I shook my husband from sleep, sobbing hysterically, convinced that by eating a few pieces of feta cheese I had irreversibly damaged our babies.

I had read that some cheeses could harbor a bacterium called Listeria that causes birth defects. But I rebelled. All these prohibitions directed at my most innocent pleasures! I'd already cut out wine, coffee, sushi, bike riding, and countless other things I enjoyed. When I was six months pregnant, I got sick after gorging on a cheese plate at an office party. In the midst of my ensuing panic—would my children suffer their whole lives for one dumb, piggy move of mine?—something clicked: These fetuses weren't veteran humans. They were different, and painfully vulnerable.

Everyone knows by now that it's bad for women to smoke or drink while pregnant, but a large body of research is revealing that much more subtle influences, such as being anemic, feeling perpetually stressed, or simply getting the flu, can also harm a developing baby. "It's a new understanding of what causes vulnerability to disease," says Vivette Glover, a perinatal psychobiologist at Imperial College London.

Until recently, doctors believed that the journey from fertilized egg to baby followed unwavering genetic instructions. But a flood of new studies reveals that fetal development is a complicated duet between the baby's genes and the messages it receives from its mother. Based on those signals, the fetus chooses one path over another, often resulting in long-term changes—to the structure of its kidneys, say, or how sensitive its brain will be to the chemical dopamine, which plays a role in mood, motivation, and reward.

This new science of fetal programming, which investigates how in utero influences cause physiological changes that can linger into later life, is producing clues to mysterious disorders such as autism and schizophrenia, as well as evidence of the very early effects of stress and toxins. Scientists still don't know all the hows and whys of these fetal cues, but the when is very clear: earlier than we ever thought.

A Delicate Project

Our first nine months resonate for the next 70 or 80 years because the fetal enterprise is so enormously ambitious. In just 270 days, a single cell becomes trillions of diverse and specialized cells—that's more cells than there are galaxies in the universe. As in any construction project, events unfold in a highly coordinated sequence. Each cell not only has its own job to do, it spurs other cells to action—sending out chemical signals that tell its neighbors to divide like crazy or to self-destruct. So when something goes wrong it can set off a domino effect. Cells might not travel to their intended destination, or they might stop multiplying too soon, or, in the case of brain cells, they might fail to establish the right interconnections.

"We pass more biological milestones before we're born than at any other time in our lives," says Peter Nathanielsz, director of the Center for Pregnancy and Newborn Research at the University of Texas Health Science Center at San Antonio. "If we do not pass them correctly, there is a price to pay."

Pregnancy is a dynamic process; the fetus is attuned to its mother in many ways. It learns about the day-night cycle from her rhythm of sleep and activity. It knows her voice: A classic 1980 study showed that immediately after birth, infants prefer a recording of their own mother reading a book over that of another woman reading the same story. The fetus even comes to appreciate its mother's taste in food after swallowing gallons of amniotic fluid tinged with those flavors. "The fetus is already a learning organism," says Christopher Coe, a psychologist at the University of Wisconsin-Madison.

By the same token, if its mother fails to provide vital nutrients, the fetus prepares for a world of scarcity, adjusting its metabolism so that it can wring the most out of every calorie. Such a baby might be born with a liver and pancreas that have less capacity to process fats and sugars, predisposing the adult to high cholesterol levels and diabetes. If the mom's stress hormones are high, her baby prepares to enter a harsh world—recalibrating its brain and nervous system to be on high alert for potential threats. As the years pass, the alterations that took place in the womb—especially when coupled with an unlucky genetic inheritance, a troubled upbringing, or an unhealthy lifestyle—may lead to problems: Heart attack. Diabetes. Osteoporosis. Depression. Schizophrenia.

Frazzled Origins

The womb experience helps establish a child's emotional resilience and susceptibility to disease, and unfortunately, that experience is not always completely under the mother's control.

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