Fears that chemical byproducts resulting from purifying drinking water with chlorine boost the chances that pregnant women will miscarry were not supported by the results of a major new study. If such threats exist at all, which is uncertain, they likely are modest, it concludes.
The national study, directed by University of North Carolina at Chapel Hill scientists, contrasts with earlier, less detailed work done in Northern California and published in 1998. That research suggested an association between byproducts known as trihalomethanes and loss of pregnancy.
"We think our new work should be an important contribution to policy studies," said principal investigator Dr. David A. Savitz of the UNC School of Public Health. "While it is not the final answer, what we found is largely reassuring relative to what had come before.
"The vast majority of the U.S. population is living with these exposures to drinking water byproducts," Savitz said. "If they clearly increased women's miscarriage rates, that would be a very big, very expensive problem to solve. Reducing exposure would be quite expensive for the water utilities and ultimately their customers."
The methods used in the new work make it the most ambitious and sophisticated study ever done on this issue, he said.
Savitz, Cary C. Boshamer distinguished professor and chair of epidemiology, and colleagues released a report on the investigation today (July 29). The American Water Works Association Research Foundation, a non-partisan, non-profit research group, sponsored it.
Others involved include Dr. Philip C. Singer, professor of environmental sciences and engineering and co-principal investigator, and Drs. Katherine E. Hartmann of obstetrics and gynecology and epidemiology, Amy H. Herring of biostatistics and Howard S. Weinberg of environmental sciences and engineering.
The scientists selected and repeatedly tested three properly functioning water purification facilities, including one with moderate levels of chlorinated disinfection byproducts, one with moderate levels of brominated disinfection byproducts and one with low levels of all disinfection byproducts. None of the utilities was selected because of water quality or health problems.
Between December 2000 and April 2004, the team recruited 3,132 women in the three areas who were planning a pregnancy or who had been pregnant for fewer than 12 weeks. They collected extensive information on the volunteers, including their patterns of water use such as drinking and bathing and what later happened with their pregnancies and births. Among tests the women underwent were ultrasound examinations to collect more detailed information about their pregnancies.
Researchers then, after adjusting for such factors as age, education, alcohol use and prior pregnancy histories, analyzed the data to see what effects the byproduct compounds might have had on pregnancy loss (miscarriage).