It is already known that drinking during pregnancy can affect the growing baby's brain and development. But different amounts of alcohol drunk at different times in a pregnancy may have different effects.
A recent study found that the children of mothers who binge drank during the first trimester in particular were more likely to have lower reading scores.
Further, children were twice as likely to have poor writing test scores if their mothers binge drank in the third trimester.
These researchers found that children's later learning problems depended on how much their mothers drank while pregnant and when in the pregnancy they drank.
The study, led by Colleen M. O'Leary, PhD, MPH, of the Centre for Population Health Research at Curtin University in Australia, looked more closely at the ways alcohol use during pregnancy could affect children.
The researchers analyzed data from a large study in Australia that involved 4,056 babies born between 1995 and 1997 to non-Aboriginal Australian women.
The researchers compared the alcohol use habits of the women during pregnancy to their children's scores on math, reading, spelling and writing tests when the children were 8 to 9 years old.
The women had reported information about how often they drank and how much they drank (per day and overall) during each trimester. They also reported how much they drank during the three months before they became pregnant.
The women who did not drink at all during pregnancy but had drunk alcohol before becoming pregnant were used as the comparison group for those who drank alcohol during pregnancy.
Of the 41 percent of the mothers who did not drink at all during pregnancy, one third of them had been drinkers before becoming pregnant.
The women who drank during pregnancy were classified into one of four groups:
- low drinking (1-2 drinks at a time fewer than 7 days a week)
- moderate drinking (3-4 drinks at a time for no more than 7 days a week)
- binge drinking (more than 5 drinks at a time, fewer than four times a month)
- heavy drinking (more than 7 drinks a week, including at least weekly binge drinking)
A drink in Australia has 10 grams of alcohol, which translates in the US to approximately 11 ounces of beer, 3.4 ounces of wine or one ounce of straight liquor.
Overall, 17 percent of the mothers did not drink during the first trimester but did drink toward the end of their pregnancy. Further, 8 percent drank during the first trimester but not during the end of the pregnancy.
These differences led the researchers to look at the effects of drinking in the first trimester compared to the third trimester.
The researchers found that the children of women who drank heavily during the first trimester were twice as likely to not meet the grade level benchmarks for reading scores, after taking into account other characteristics of the women and their children.
In raw numbers, 9 percent of the children whose mothers drank heavily during the first trimester did not meet the reading benchmark, compared to 4 percent of the children of mothers who drank before but not during pregnancy.
"Occasional binge drinking at any stage during pregnancy was also associated with a higher percentage of children not achieving the benchmark in spelling and writing," the researchers wrote.
In addition, mothers who occasionally binge drank in their third trimester were more than twice as likely to see their children miss the writing benchmark score.
Meanwhile, however, the children of moms who drank low and moderate amounts during pregnancy tended to do a little better on all four standardized test subjects when compared to the children of women who drank before but not during pregnancy.
The children of mothers who drank low amounts during the first trimester were 27 percent less likely to miss the math benchmark than the children of mothers who drank before but not during pregnancy.
These children of low and moderate drinkers may have had slightly better performance due to differences in the women's level of education and/or income.
Women who did not complete high school were more likely than those with a degree to binge drink occasionally in their third trimester.
Women with a high household income were most likely to be low or moderate drinkers than other income groups.
Low-income women were more likely than high-income women to not drink during pregnancy at all.
"Factors crucial to a child’s educational achievement include contributions from the child, home, school, teacher, curricula, and teaching approaches, and these need to be taken into account when examining educational achievement," the authors wrote.
The study was published July 8 in the journal Pediatrics. The research was funded by Healthway (the Western Australian Health Promotion Foundation), the Australian National Health and Medical Research Council Public Health Fellowship, Curtin University and the Western Australian Drug and Alcohol Office. The authors declared no conflicts of interest.