Dr. Calvin Hobel, a perinatologist in Los Angeles, has spent much of hiscareer trying to document the effects of stress on pregnancy and to figure outhow best to get pregnant women to relax. Not only does he see the importanceclinically, but he's reminded of it daily.

Beginning with his 45-minute commute to Cedars Sinai Medical Center, Dr.Hobel watches women putting on makeup in their cars, wolfing down bites ofbreakfast ... and the clincher? Pregnant women who come to yoga classes tolearn how to relax have to take a breather -- to answer cell phones they justcouldn't leave behind.

Stress is such a familiar part of women's lives that many just squeeze apregnancy right into all the hubbub. Even if women wonder whether it's bad fortheir developing fetuses, it's often hard to get a straight answer, mainlybecause most doctors don't know how much stress is too much -- or for whom.

But researchers, including Hobel, are getting closer to unlocking themystery.

For one thing, a growing number of studies are confirming what used to beconsidered just an old wives' tale -- that stress really isn't good forpregnant women. It not only increases the risk of pre-term labor, but possiblya host of other problems for babies after birth.

Even more important -- and clearly more difficult to discern -- researchersare close to being able to predict who's most susceptible to stress and athighest risk for complications, such as pre-term birth. In fact, some say itwon't be long before health-care providers have the tools to head off theseproblems before it's too late.

"Stress is a silent disease," says Dr. Hobel, director ofmaternal-fetal medicine at Cedars Sinai and a professor ofobstetrics/gynecology and pediatrics at University of California, Los Angeles(UCLA). "Pregnant women need to be educated in recognizing when they havestress, the consequences and some of the simple things they can do to make adifference."

Throw Out the 'Blueprint'

Developmental biologists once thought fetuses were conceived with a"blueprint" from their parents' genes. As long as you gave the growingfetus the right nutrients and avoided harmful substances, this blueprint woulddevelop into a healthy baby. That's not what experts believe anymore, says Dr.Pathik Wadhwa, assistant professor of behavioral science, obstetrics andgynecology at University of Kentucky College of Medicine.

"This view has more or less been completely turned upside down,"says Dr. Wadhwa, who is co-editing a special issue of scientific papers onpregnancy and stress to be published in Health Psychology next year."At each stage of development, the organism uses cues from its environmentto decide how best to construct itself within the parameters of itsgenes."

Stress is an example of how a fetus responds to stimuli in the womb andadapts physiologically. "When the mother is stressed, several biologicalchanges occur, including elevation of stress hormones and increased likelihoodof intrauterine infection," Dr. Wadhwa says. "The fetus builds itselfpermanently to deal with this kind of high-stress environment, and once it'sborn may be at greater risk for a whole bunch of stress-relatedpathologies."