Air pollution, fetuses, and babies. (Pregnancy & Birth).

A growing body of research from around the world suggests that smog is exacting a much greater toll than previously known on infants and unborn babies.

Scientists have known that the high levels of air pollution found in the developing world can harm babies, and that lesser pollution in United States' cities can sicken or kill the elderly and infirm.

It was always assumed the fetus was isolated in the womb from things in the environment. Research has found that pollutants inhaled by pregnant mothers can reach fetuses through the umbilical cord.

In a 1998 study of pregnant women in Sao Paulo, Brazil, scientists found that women exposed to high levels of nitrogen and sulfur oxides were 18 percent more likely to have their pregnancies end in stillbirths. Nitrogen and sulfur oxides, produced by fuel combustion in vehicles and factories, is more abundant in Sao Paulo than in US cities.

The Sao Paulo researchers also found evidence of carbon monoxide in the umbilical cords of 47 nonsmoking mothers. The levels of carbon monoxide rose and fell with daily air pollution levels. Carbon monoxide can cut off oxygen to a fetus, leading to death.

The discovery of carbon monoxide in umbilical cords helps explain how air pollutants reach a fetus and cause damage.

New research supports the possibility that the harmful effects of dirty air can extend into the womb. Over a dozen studies in the United States, Brazil, Europe, Mexico, South Korea, and Taiwan have linked smog to low birth weight, premature births, stillbirths, and infant deaths. In the United States, research has documented ill effects on infants even in cities with modern pollution controls.

Most of the studies have been analyzed by a peer review and have been published in leading journals (or will be soon). The studies disagree on which pollutants are of most concern. Some implicate gases, others blame particles, and some point to both.

In the latest research from University of California in Los Angeles (UCLA), Beate Ritz, an epidemiologist at UCLA's Center for Occupational and Environmental Health, found that women exposed to high levels of ozone and carbon monoxide were three times more likely than others to have babies with cleft lip and palate and defective heart valves.

The study, to be published in the American Journal of Epidemiology, found that the greatest risk occurs during the second month of pregnancy, when a fetus develops most of its organs and facial structure.

Virtually the entire study area met federal standards for carbon monoxide; much of the region complied with ozone requirements.

"We do see the trend. There is a growing body of literature finding an association between conventional air pollution and infant mortality and morbidity," said John D. Bachmann, associate director of science policy in the EPA's air division.

The EPA is weighing the emerging body of research as it considers whether to tighten its standards for airborne particles.

--Los Angeles Times, December 16, 2001