Season of Conception Linked to Academic Performance


Whether it was a steamy July night or a chilly January morning, the season in which a child is conceived could affect its future academic achievement, suggests a new study.

Children conceived June through August scored lower than other kids on math and language tests in Indiana, said researcher Paul Winchester, a neonatologist at Indiana University School of Medicine.

Winchester and his colleagues speculate the link has to do with mothers' and in turn fetuses’ exposure to the high pesticides used during summer months, a cause-and-effect that has yet to be proven.

“The pesticides we use to control pests in fields and our homes and the nitrates we use to fertilize crops and even our lawns are at their highest level in the summer," said Winchester, who presented his research today at an annual meeting of the Pediatric Academic Societies in Indianapolis.

It’s no secret that parents yearn to find the recipe for that perfect baby boy or girl. And tricks abound: The sweet sounds of Mozart streaming through a mom-to-be’s tummy or schooling little Suzy as soon as she can manage to sit up on her own are just a few tricks touted and parent-tested for the perfect offspring.

Winchester's study suggests planning the date of an egg's fertilization could be added to the mix.

Brainy babies

Winchester and his colleagues studied more than 1.5 million Indiana students in grades 3 through 10 who took the Indiana Statewide Testing for Educational Progress (ISTEP) exam. They charted the students’ test scores with the month in which each student had been conceived.

They found a statistically significant correlation between the ISTEP scores for math and language and the season of conception, with June through August dates linked with the lowest scores.  

The correlation between test scores and conception season held regardless of race, gender (apparently, girls score higher on these tests than do boys) and grade level—lower grade-level students tend to score lower than higher grade levels.

Streams and other bodies of water in the area showed a stark jump in pesticides , such as atrazine, and fertilizer chemicals, such as nitrates, during the summer months as well.

Pesticide link

Winchester suggests that exposure to pesticides, and other agriculture-related chemicals, is to blame for the lower cognitive performance of the summer-made babies. Converging lines of evidence, he said, make this explanation plausible.

For instance, a past study found that pregnant women exposed to pesticides were more likely to develop hypothyroidism, a condition in which they produce low levels of thyroid hormones.  

In addition, “it’s been established for over a decade that pregnant women carrying their child who have low thyroid levels are more prone to having children with cognitive performance issues,” Winchester said.

Thyroid hormones are critical to how well the brain functions, to the point where hospitals now run screening of newborns to check their thyroid levels.

“What we didn’t realize is many of the ultimate outcome scores of these children was just as dependent on the mothers’ level of thyroid in the first trimester as it was on the baby’s levels at birth,” Winchester told LiveScience.

That’s because the fetal brain is developing before the fetus has formed a thyroid gland. “So [the fetus] is actually developing nervous tissue, the parents of all future neurons, at a time when it’s the mother’s thyroid the fetus depends on,” Winchester said.

Birth defects

Winchester said that the study has its weaknesses, including that his team only studied children in Indiana so the results cannot be generalized to the rest of the nation. "While our findings do not represent absolute proof that pesticides and nitrates contribute to lower ISTEP scores, they strongly support such a hypothesis," Winchester said.

Results could be bolstered, he said, if the scientists could get birth-certificate information about the infants and their parents, including whether the mother smoked and precisely where the babies were born.

Also the Pediatric Academic Societies meeting, Winchester reported that birth defects in Indiana and the U.S. as a whole maxed during April through July.

Birth defects are the leading cause of infant deaths in the United States, accounting for more than 20 percent of infant deaths, according to the Centers for Disease Control and Prevention. However only some states are mandated to collect birth-defect information. “How is it that 16 states were not even counting birth defects as of 2001?” Winchester said.

Jeanna Bryner
Live Science Editor-in-Chief

Jeanna served as editor-in-chief of Live Science. Previously, she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a graduate science journalism degree from New York University. She has worked as a biologist in Florida, where she monitored wetlands and did field surveys for endangered species. She also received an ocean sciences journalism fellowship from Woods Hole Oceanographic Institution.