Women exposed to the chemical bisphenol A (BPA), which is found in many plastic products, during pregnancy give birth to lower-weight babies than moms not exposed, according to a new study of workplace exposure in China.

Contact with BPA even had an effect on the child's weight if just the father, and not the mother, was exposed at work while the woman was pregnant, although the effect was smaller. However, the researchers say the results may only hold for high levels of BPA, like those found in factories that manufacture the chemical, with low-exposure effects remaining less clear.

The study, one of the first to link BPA with low birth-weight in humans, adds to the growing body of evidence questioning the safety of BPA, the researchers say. The chemical has been shown to leach from plastic products, food cans and dental sealants . A mother's exposure to the chemical has also been linked with an increased risk of wheezing in children . While the U.S. Food and Drug Administration said in 2008 that products containing BPA are safe, the organization has since expressed concerns about BPA and is conducting studies, along with other government organizations, to discern any harmful effects of BPA.

BPA in the workplace

The researchers collected information from more than 1,000 factory workers in China between 2003 and 2008. Participants worked either in factories that manufactured BPA or in factories in which they had no exposure to BPA.

Participants were asked to recall how long they worked in the factory while the woman was pregnant. The researchers sampled the air at the factories to calculate how much BPA the pregnant mother would have been exposed to.

On average, mothers worked for three months in the factory while they were pregnant .

Babies of mothers exposed to BPA at work weighed, on average, 0.4 pounds (168.4 grams) less than babies whose mothers weren't exposed. Babies whose moms had the highest exposure to BPA in the workplace weighed about half a pound (235 grams) less.

If just the father was exposed to BPA at work, babies weighed, on average, 0.2 pounds (90.7 grams) less. A pregnant woman might be exposed to BPA by touching his contaminated clothes, visiting her spouse or living close to the manufacturing factory, the researchers say.

Reproductive effects

BPA is an endocrine disruptor, meaning it can interfere with the production or action of hormones in the body. It has already been shown to have an effect on human reproduction. A study last year found that exposure to even low levels of BPA can reduce sperm quality in men.

The researchers note their new study involved a relatively small number of people and the results were based on participants' recollection of their time during pregnancy, which they may not have remembered accurately. Future research is needed to better understand the effects of BPA during pregnancy, the researchers say.

The study, conducted by researchers at the Kaiser Permanente Division of Research in Oakland, Calif., was published in the current issue of the journal Reproductive Toxicology.

Pass it on: Exposure to BPA in the womb may decrease a baby's birth weight.

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