No question, the evidence that heavy drinking during pregnancy is risky is incontrovertible.
Fetal alcohol spectrum disorders (FASDs), which affect babies born to mothers who drank heavily while pregnant, involve physical as well as behavioral and learning problems. Organizations such as the Centers for Disease Control and Prevention, the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics say there is no safe amount of alcohol to drink while pregnant.
But what does the scientific evidence actually say about drinking an occasional glass of wine or bottle of beer while pregnant?
Not much, according to a recent paper in the journal BMJ Open. The authors reviewed 24 studies about light drinking in pregnancy and pooled their results.
Evidence about the effects of drinking the equivalent of two pints of beer or two small glasses of wine per week is “sparse,” the researchers concluded. “Our extensive review shows that this specific question is not being researched thoroughly enough.”
But, as the authors of the paper note, absence of evidence is not the same as evidence of absence. In other words, just because scientists haven’t investigated whether light drinking in pregnancy is risky doesn’t mean that it isn’t. After all, there’s no evidence that it’s safe, either.
“Ours was a very comprehensive systematic review of all the high-quality studies on this topic, and we didn’t find any evidence of a beneficial effect,” co-author Luisa Zuccolo, a senior research fellow in epidemiology at the U.K.’s University of Bristol, told me. “If anything, there was some evidence of harm for outcomes such as being born small for gestational age and being born preterm.”
Until recently, though, U.K. guidelines advised women to avoid drinking alcohol while trying to conceive or during the first trimester but didn’t proscribe it altogether, even though animal studies have shown that the fetal brain is susceptible to the effects of alcohol at virtually every stage of development. The guidelines, published in 2008, advised women not to drink more than the equivalent of one or two glasses of wine or bottles of beer in a week.
But in January 2016, the U.K. Department of Health published new alcohol guidelines that state the safest approach for women who are considering getting pregnant or are pregnant is not to drink alcohol at all.
Zuccolo called such advice “spot on.”
“Most countries follow the precautionary principle when advising on fetotoxic substances,” she said. “The reason is that we don’t know what levels are safe, plus, they are likely to differ from baby to baby, so no point in risking it. The only surely safe level is no alcohol.”
I asked Zuccolo why scientists haven’t conducted more research into the effects of drinking small amounts of alcohol during pregnancy. “I think many studies have been published that look at the whole spectrum of drinking, not just light drinking, and some looked at light and moderate drinking combined, but very few focused on the dose we were interested in, which is very small amounts.”
Meanwhile, despite the solid evidence about the risks of drinking heavily while pregnant, some women still do, researchers reported recently in the journal Reproductive Toxicology. Based on a comprehensive search of the scientific literature for quantitative research about binge-drinking during pregnancy, they estimated how common it was in different countries.
They found that the percentage of pregnant women who had at least one drinking binge, defined as four or more standard alcoholic drinks per occasion, ranged from 0.2% in Singapore and Brunei Darussalam to 13.9% in Paraguay.
The United States was closer to Singapore and Brunei Darussalam than to Paraguay, Shannon Lange, the first author of the study and a PhD candidate at Toronto’s Center for Addiction and Mental Health, told me.
Based on 19 studies, Lange and her collaborators estimated that in the United States, 3.1% of pregnant women binge on alcohol, representing about a fifth of the 14.8% of pregnant women who consume at least one drink. Interestingly, in the United Kingdom, where guidelines until recently didn’t totally ban the practice, approximately 40% of pregnant women have at least one drink, and roughly 8% or 9% of them binge drink, according to Lange’s study.
“The findings of the current study are alarming and have significant long-term implications, as FASD (fetal alcohol spectrum disorders) is a lifelong disability,” Lange and her coauthors wrote.