When researchers linked standardized test scores of 1,667,391 Indiana students in grades 3 through 10 with the month in which each student had been conceived, they found that children conceived May through August scored significantly lower on math and language tests than children conceived during other months of the year.
The correlation between test scores and conception season held regardless of race, gender, and grade level...The lower test scores correlated with higher levels of pesticides and nitrates in the surface water (nearby streams and other bodies of water) during that same time period.
"Exposure to pesticides and nitrates can alter the hormonal milieu of the pregnant mother and the developing fetal brain," Winchester explained in a statement. For example, past research has linked exposure to pesticides and nitrates to low thyroid hormone levels ("hypothyroidism") in pregnant women and hypothyroidism in pregnancy has been tied to lower intelligence test scores in offspring.
While the current findings do not prove that pesticides and nitrates contribute to lower test scores, "they strongly support such a hypothesis," Winchester said.
"A priori there should be no reasons particularly why the month of conception should change your (test) scores," he added in an interview, "and yet from our chain of evidence our hypothesis was that if pesticides do alter the friendly environment of the developing fetus than that might be reflected in lower scores. And unfortunately that's what we found."
"There is something going on" and it needs to be studied further, Winchester concluded.
I looked at birth rates by month (2002 was the most recent data I viewed)---there's not a wide variety within the year. There's a low of 13.7 live births per 1000 people in June and a high of 14.1 for July. (Rates for just Indiana mirror the national data.) Assuming rates have been fairly consistent, then the number of kids entering school each year should be evenly spread out in terms of birthdays. I would have thought it would be the June, July, and August babies that scored lower more often as they are the youngest in their classes.
Correlation, of course, is not the same as causation. My guess is that the amount of ice cream consumed or the increased number of backyard barbecues during the same months of the conceptions noted could be correlated with the testing data. It's hard to tell from the article if there is more evidence available that makes the link between pesticides and test scores in later years seem linked. As always, I guess we'll just have to stay tuned for more news as it happens.