March 27, 2009 -- New research shows that babies conceived in the spring and early summer have a higher risk for a wide range of birth defects, including Down syndrome, cleft palate, and spina bifida.
The reported increase in birth defects was modest, but it coincided with a similar spike in groundwater pesticide levels during the spring-early summer planting season.
These findings suggest that pesticide exposure may influence birth outcomes nationwide, researchers say.
“There appears to be a season of conception in which the risk of having a child with a birth defect is higher,” Indiana University School of Medicine neonatology professor Paul D. Winchester, MD, tells WebMD.
“This study does not prove that pesticides cause birth defects, but we set out to show that they did not and we were not reassured.”
Pesticide Levels Measured in Water
In earlier studies, researchers have reported increases in birth defects, pregnancy complications, and miscarriages in babies born to farm workers with high levels of exposure to agricultural pesticides.
But the study is one of the first to suggest that indirect exposure to agricultural chemical may influence birth outcomes.
Winchester and colleagues compared data on pesticide levels in surface water between 1996 and 2002 to data on birth defects at the national level during the same period.
The researchers used the U.S. Geological Survey’s National Water Quality Assessment (NAWQA), which includes samples from 186 streams across the United States, representing 50% of the drinking water consumed in the country.
Statistics on birth defects were reported to the CDC by individual states.
The NAWQA analysis confirmed that concentrations of widely used pesticides in ground water were highest in the months of April through July during the period examined.
During this same period, women who conceived in these months were about 3% more likely to deliver a baby with a birth defect than women who conceived in other months, Winchester says.
“That doesn’t sound like much, but at a population level it could mean thousands of additional birth defects,” he says.
Prospective Study Under Way
Winchester adds that inconsistent recording of birth defects from state to state during the time the data were collected probably resulted in an underestimation of birth defects.
During this time, 13 states and the District of Columbia had only passive birth defects surveillance programs.
March of Dimes medical Director Alan R. Fleischman, MD, tells WebMD that even with the limitations, the study raises important questions about the impact of environmental chemical exposures on birth outcomes.
“There is a limit to what you can imply from this type of study,” he says. “But it does focus attention on an important issue.”
Fleischman chairs the advisory committee for the National Children’s Study, the largest prospective study ever in the U.S. to examine the effect of environmental influences on children’s health.
Researchers are now recruiting women for the trial. The goal is to follow 100,000 children nationwide from conception to age 21.
“We will certainly be measuring exposure to environmental chemicals before conception and during pregnancy,” he says. “This is not easy to do, but it is important to better understand the relationship between chemical exposures and birth outcomes.”