Don't blame me for the title, but perhaps it's best that Ohio State University researchers politely stated their study result as thus:
Women who are obese before they become pregnant are at higher risk of having children with lower cognitive function - as measured by math and reading tests taken between ages 5 to 7 years - than are mothers with a healthy prepregnancy weight, new research suggests. [...]
The researchers calculated the mothers’ body mass index (BMI) based on their reported heights and weights. More than half of mothers had normal BMIs before pregnancy, and 9.6 percent were obese, meaning they had a BMI of 30 or higher.
Controlling for all other variables, the analysis showed that maternal prepregnancy obesity was negatively associated with math and reading test scores. Children of obese women scored, on average, three points lower on reading and two points lower on math than did children of healthy-weight women. The mean reading score among all the children was 106.1 points and the mean math score was 99.9.
Though the score differences seem small, Tanda noted that these effects of prepregnancy obesity were equivalent to a seven-year decrease in the mothers’ education and significantly lower family income, two other known risk factors that negatively affect childhood cognitive function.
Second, "Though the score differences seem small, Tanda noted that these effects of prepregnancy obesity were equivalent to a seven-year decrease in the mothers’ education and significantly lower family income" seems to be the real indicator.
though, "two other known risk factors that negatively affect childhood cognitive function" this should be "correlated", not "affect", right? They don't know which is the cause and which is the result.