April 2, 2009
Birth defects linked to seasons
U.S. birth defect rates are highest for women conceiving in the spring and summer, researchers at the Indiana University School of Medicine have found.
Dr. Paul Winchester, the lead author, said the researchers also found that this period of increased risk correlated with higher levels of pesticides found in surface water across the United States.
Studying all 30.1 million births in the United States between 1996 and 2002, the researchers found a strong association between the increased number of birth defects in children of women whose last menstrual period occurred in April, May, June or July and elevated levels of nitrates, atrazine and other pesticides in surface water during the same months.
Many of these chemicals -- including the herbicide atrazine, which is banned in European countries but permitted in the United States -- are suspected to be harmful to the developing embryo. This is the first study to link their increased seasonal concentration in surface water with the peak in birth defects in infants conceived in the same months, Winchester said.
The correlation between the month of last menstrual period and higher rates of birth defects was statistically significant for half of the 22 categories of birth defects reported in a Centers for Disease Control database from 1996-2002, including spina bifida, cleft lip, clubfoot and Down's syndrome.
The findings are published in the medical journal Acta Paediatrica.