As a physician, Tamar,* of Denver, Colorado, knew to stay away from drugs, alcohol, and cigarettes during pregnancy. But upon learning she was pregnant for the first time, the normally laid-back doctor suddenly felt anxious about her everyday surroundings. Spooked by recent headlines linking birth defects to everything from smoggy air to microwave ovens, she felt guilty drinking tap water and avoided household chores out of fear that cleaning products would harm her growing fetus.

"On the one hand you feel so blessed," she said. "But at the same time, you look around and you worry -- is it safe?" Protective instincts naturally kick in when you're pregnant, and every mother-to-be wants to ensure her baby is as healthy as possible. But where is the line between prudent caution and paranoia? How far should you go to avoid risks, in light of media reports that raise questions about hazards in our everyday environment?

Experts in teratology (the branch of science devoted to harmful effects on a fetus) say protecting your unborn baby doesn't mean turning your life upside down. In fact, they say, getting too stressed-out about tiny, theoretical risks isn't healthy either.

"In general, there is a tendency for women to be very alarmed," says Gideon Koren, M.D., director of Motherisk, a teratology information service based at the Hospital for Sick Children in Toronto. "The media and other sources often highlight bad things and ignore studies that are reassuring. It leads a lot of women to have high levels of anxiety and avoid small pleasures."

Consider these statistics: 1 to 3 percent of babies will be born with a birth defect, usually the result of a genetic abnormality. Just 5 percent of these cases have a known "environmental" (non-genetic) cause, and of those, half are due to the effects of uncontrolled preexisting diabetes on the developing fetus, according to Lynn Martinez, manager of the Birth Defects and Genetics Program at the Utah Department of Health. Most of the rest involve risks such as infections, poor nutrition, cigarettes, alcohol, and prescription or recreational drugs.

"If a mother is not actually poisoned by an outside toxin, the evidence for increased risk for any kind of problem just isn't there," said Martinez. "Even though only 5 percent of birth defects have any kind of known environmental cause, we get 10,000 calls a year here. And that's what they're calling about."

At the same time, activists point out that we don't know enough about the effects of many chemicals and pollutants on pregnancy. And since a fetus is growing at an astonishing pace during its nine months in the womb, it's not unreasonable to worry that a small amount of toxin could disrupt the exquisitely orchestrated process.

Activists like Daniel Swartz of the Children's Environmental Health Network in Washington, D.C., suggest pregnant women err on the side of caution and try to reduce their exposure to cleaning solvents, air pollution, and unfiltered tap water.

But even Swartz says that the potential hazards in our normal environment pale in comparison to well-known risks like mercury, cigarettes, alcohol, drugs, and lack of prenatal care. "In the grand scheme of things, taking your prenatal vitamins is likely to be more important," he said. To reassure moms-to-be, BabyTalk canvassed experts to separate reality from rumor. Here's what we found.

Ulysses Torassa is the health writer for the San Francisco Chronicle.

---