Drinking water that contains disinfection by-products at regulatory cut-off levels does not appear to raise a pregnant woman's risk of delivering a small baby or delivering prematurely, new research shows.

Previous studies that have suggested adverse pregnancy outcomes in women exposed to drinking water disinfection by-products "are limited by poor exposure assessment," the researchers note in the journal Epidemiology.

In the new study, funded in part by the US Environmental Protection Agency, researchers used improved exposure data to more accurately calculate the potential risks. Throughout the study, the researchers collected weekly or biweekly water samples at representative location in the water distribution system of three US communities.

In analyses involving more than 3800 pregnant women, Dr. Caroline S. Hoffman from the University of North Carolina at Chapel Hill and colleagues found no link between exposure to drinking water disinfection by-products -- in particular, total trihalomethanes (TTHMs), haloacetic acids, and total organic halides -- and any increased probability of delivering a small "growth restricted" baby or delivering a low birth weight baby.

According to the investigators, the results do not support a harmful effect of residential TTHM or haloacetic acid levels within the regulatory limits on fetal growth. In addition, none of the individual TTHM or haloacetic acid types was consistently associated with fetal growth restriction.

A possible association between TTHM and delivery of a small baby was evident only for average residential concentrations above the current regulatory standard, Hoffman and colleagues found.

Their research, they add, also provides evidence that exposure to high levels of these drinking water disinfection by-products does not increase the likelihood of delivering preterm, before 37 weeks of pregnancy.

SOURCE: Epidemiology, September 2008.