Light drinking during pregnancy can alter the fetal brain: study

  • A small new study suggests that as little as one alcoholic drink per week affects the structure of a fetus’s brain.
  • The research is the first to use fetal MRI to see how drinking affects a fetus in real time.
  • Recommendations against light drinking during pregnancy have been criticized as paternalistic rather than evidence-based.

A new study suggests that having less than one alcoholic drink per week during pregnancy is enough to change the fetal brain in ways that can lead to problems once the baby is born, such as language deficits.

The yet-to-be-published study, which will be presented at the Radiological Society of North America annual meeting next week, used fetal brain imaging to see how alcohol consumption in pregnant women might affect key regions of the developing brain.

The findings suggest that even occasional drinking can slow fetal brain development and alter the part of the brain that helps babies develop social skills, interpret sights and sounds, and understand language.

While previous research shows that heavy drinking during pregnancy can lead to permanent and serious physical, cognitive, and behavioral problems in babies, the edicts that even light drinking is dangerous have come under increased scrutiny from some doctors and parenting experts.

The study authors told Insider that their research is the first to use this type of technology to see when and where exposure to alcohol begins to affect the developing brain.

And while not all, or even most, babies of pregnant women will experience problems, researchers say there’s no guarantee that babies won’t, either.

“There may be a very small risk associated with every cup you might drink during pregnancy, but you never know if that’s what pushes you over the edge,” co-author Dr. Marilyn Stumpflin told Insider.

The researchers studied 24 brains out of an initial 500 to eliminate confounding factors

To conduct the study, doctors from the Medical University of Vienna in Austria assembled a group of 500 women who were receiving fetal MRIs for various clinical reasons. Then they narrowed that group down to 51 who said they had consumed some alcohol during their pregnancy in an anonymous questionnaire. This is about 10%, which is in line with previous estimates of the number of pregnant women who drink.

(The researchers told Insider that a psychiatrist was involved in the recruitment process, which emphasized making the environment a safe place for people to share honestly about their drinking habits.)

Next, the doctors excluded all mothers whose fetuses might have abnormal brain structures for reasons other than alcohol, such as heart disease, genetic abnormalities, or imaging errors. This left them with 24 fetal MRIs of drinkers to compare with fetal MRIs of non-drinkers at the same stage of pregnancy: between 22 and 36 weeks.

“We’re really focused on creating a very structured, very unbiased data set and patient cohort,” said Stuempflen.

The study authors found that the brains of heavy drinkers were developing much more slowly than the brains of non-drinkers of the same gestational age. They also found that the right superior temporal sulcus, which plays a role in empathy, point-taking, language perception, and more, was shallow.

Specifically, the doctors noticed that the heavy drinkers’ brains were smoother and more symmetrical, while normally developing brains had more folds, and one hemisphere grew earlier than the other.

Differences in the brains of fetuses exposed to alcohol

The fetal brain exposed to alcohol (left) has the smoothest cortex in lobes observed. In the healthy control (right), the superior temporal sulcus (see arrows) is already forming.

Patrick Kinnast



“The most surprising thing to me is that fetuses who were exposed to a relatively low amount of alcohol developed this symmetrical brain,” study senior author Dr. Patrick Kienast told Insider. “That means as little as one drink a week, we’ve already seen these effects.”

The study builds on the group’s work presented last year, which found that fetal brains exposed to alcohol had a smaller paraventricular region (the “birthplace” of all neurons, Stimpflin said) and a larger corpuscle (the highway between the two cerebral hemispheres). from the fetus. A brain that has not been exposed to alcohol.

Because fetal alcohol spectrum disorder can present so differently in all patients — from mild attention difficulties to noticeable facial abnormalities to learning disabilities and birth defects — it makes sense that alcohol affects these broad brain structures rather than a single contained region, Stuempflen said.

Her team plans follow-up research to see if and how these changes affect children as they grow.

There is growing evidence linking alcohol consumption during pregnancy to fetal brain changes

The CDC, the American College of Obstetricians and Gynecologists, and the American Pediatric Association all stress that there is no known safe amount of alcohol during pregnancy. The World Heart Federation goes so far as to say that there is no safe amount of alcohol for anyone, pregnant or not.

But laws that completely eliminate alcohol during pregnancy have been criticized as paternalistic rather than evidence-based, since it is difficult to conduct high-quality studies on the harms of light alcohol consumption during pregnancy.

Such studies often must rely on mothers honestly remembering how much they drank many years before, and it is not possible to separate all of the many factors—diet, exercise, health care access, stress, sleep, and social support, for example. The example is not limited to. It can affect the development of the child.

Previous imaging studies have been done in mice, or done retrospectively, like this 2020 paper concluding that just one reported drink per week results in changes in the developing brain that can lead to behavioral defects in children.

There are no studies that find a link between light or moderate alcohol consumption and growth challenges in children. Parenting expert and economist Emily Oster pointed to one Danish study, for example, which found that up to eight drinks per week during pregnancy had no effect on children’s levels of intelligence or attention.

The Kienast team stresses that the potential risk of drinking, even if it’s low, isn’t worth it. “We know that prenatal exposure to alcohol is the most important contributing factor to preventable cognitive impairments in children and, later, adults,” Stumpflin said.

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