Drinking low to moderate amounts of alcohol during pregnancy may not have any damaging developmental effects on children five years later, according to new research published Tuesday.
But, the authors stressed, pregnant women should still err on the side of caution and avoid alcohol altogether, since no safe level of alcohol consumption has been established.
In a series of five studies, Danish researchers statistically evaluated how different levels of drinking during pregnancy affected the five-year-old children of 1,628 women. They compared women who drank 0, 1 to 4, 5 to 8 and more than 9 drinks per week while they were pregnant and assessed their children's IQ, attention span and their capacity for what are known as executive functions, which include organization and planning.
Children whose mothers reported having 1 to 4 or 5 to 8 drinks per week while pregnant did not perform any worse on tests measuring IQ and executive functions. Binge drinking, which meant having 5 or more drinks in one sitting, also did not have any significant negative effect on children five years later.
Drinking more than nine drinks per week, however, was linked to five-year-olds' lower attention span.
In the study, the researchers defined a drink as having 12 grams of pure alcohol. In the U.S., a drink is considered to have 14 grams of pure alcohol, according to the Centers for Disease Control and Prevention.
Despite the findings, the authors wrote that "the most conservative advice for women is not to drink alcohol during pregnancy" since there may still be adverse effects their research didn't uncover.
And in the U.S., government health agencies advocate total abstinence for expectant mothers, said Dr. Kimberly Fortner, assistant professor of maternal and fetal medicine at Vanderbilt University.
"But we know that from looking at studies and from other panels that up to 30 percent of pregnant women will use alcohol during pregnancy."
"The study investigated just a few of the many possible outcomes of low to moderate alcohol use during pregnancy," said Thomas Donaldson, executive director of the National Organization on Fetal Alcohol Syndrome. "Alcohol is known to cause birth defects such as fetal alcohol spectrum disorders (FASDs) and there are other studies suggesting harm at low levels."
"No one study takes into account the myriad of relevant factors such as maternal drinking pattern, differences in maternal metabolism, differences in genetic susceptibility, timing of the alcohol consumption during pregnancy, and variation in the vulnerability of different brain regions," said Dr. Hyagriv Simhan, associate professor of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh. "Furthermore, this study addresses outcomes at age five, but not later in childhood, and it's possible that effects may be identifiable later on but not noticed by age 5."
Alcohol may affect women differently, said Dr. Robert Marion, professor of pediatrics and director of the Children's Evaluation and Rehabilitation Center at Albert Einstein College of Medicine. Some women are more susceptible to the effects of alcohol during pregnancy, meaning that a smaller amount of alcohol could lead to problems.
"We don't know how people are going to metabolize the alcohol and don't know who's going to be more susceptible to its effects, so it's wise to lay off," he said.
But Fortner added that because every woman is different, what is recommended for one woman may not necessarily be recommended for another.
"We don't know variables for each woman to be able to interpret it for her," she said.
The first trimester is the riskiest time for expectant mothers to drink, Marion said. Alcohol can cause defects in the organs, which are still forming, as well as developmental defects during this sensitive time. The brain develops throughout pregnancy, so neurological damage caused by alcohol can occur at any point in gestation.
While some children may not have any developmental problems linked to their mother's drinking during pregnancy, an estimated 40,000 children per year are affected by FASD, a spectrum of disorders that could lead to poor growth, mental retardation, learning disabilities and other problems, according to the National Organization on Fetal Alcohol Syndrome.
"We know that FASDs are 100 percent preventable if alcohol is not consumed during pregnancy, so why take the risk?" Donaldson said.
Other experts say while they don't recommend that pregnant women drink regularly, an occasional indulgence is perfectly fine.
"I think this study will allow doctors to tell patients that an occasional drink is unlikely to be harmful to the fetus. For many women there are the occasional events (a wedding, an anniversary, etc.) when a single drink (maybe a bit of bubbly) would be very appreciated. I, for one, will say it is OK," Dr. Ian Holzman, professor of obstetrics, gynecology and reproductive science at The Mount Sinai Hospital in New York said in an email.
"Many women will have an alcoholic drink before they realize that they are pregnant, and this might be reassuring news," said Dr. Kevin Ault, an associate professor of gynecology and obstetrics at the Emory University School of Medicine.