Research has confirmed that children conceived between June through August are likely to score lower on cognitive tests. Leading researchers suggest that the cause is seasonal pesticides and nitrates, which are detrimental to brain development. The researchers found that test scores for math and language were distinctly seasonal with the lowest scores received by children who had been conceived in June through August.
Paul Winchester, M.D., professor of clinical pediatrics at the Indiana University School of Medicine. "Exposure to pesticides and nitrates can alter the hormonal milieu of the pregnant mother and the developing fetal brain."