Is light drinking during pregnancy safe?

We asked 25 experts.

Hello everyone,

I hope you are safe and well.

Even before COVID-induced binge drinking spikes, there has been a worrying rise in heavy drinking among young people, especially women. Yet, health authorities from the UK, US and Australia advise pregnant women to abstain from alcohol. But is it all that bad to have a couple of glasses of wine? And is there a safe dose?

We asked 25 experts in epidemiology, alcohol use and pharmacology. Here's what we found...

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What do the experts say..

As most of us probably know, moderate to heavy alcoholic drinking during pregnancy can lead to premature birth or even miscarriage explains Dr Loubaba Mamluk from Bristol University. It's also responsible for fetal alcohol syndrome or fetal alcohol spectrum disorder (FASD), which affects 8 kids in every thousand.

FASD results in children with growth impairment and facial abnormalities. Effects on brain function, including changes in mood and behaviour, are most concerning. FASD is the main cause of developmental disability and mental retardation, writes Prof Shiva Singh from the University of Western Ontario. This is because brain development takes place throughout the duration of pregnancy (and beyond it) writes Dr Annika Montag from the University of California San Diego, which makes it a particularly vulnerable organ.

But what about light drinking?

Greater doses carry greater risk and lighter doses are safer, say the experts. However — and you may not like this — no level of alcohol, no matter how low, has been demonstrated to be safe during pregnancy or indeed generally.

Low-to-moderate doses of alcohol disrupt behaviour and cognitive capacity. This has been shown in great detail in mice and even in monkeys. Human studies are a lot less consistent, explains Professor Molly Goodfellow from the University of Maryland, and conclusions are not as clear. An old study indeed suggested that small amounts of alcohol would do no harm. However, this has been contested as the study only looked at 5 year olds, where the brain is still developing. It is known that FASD effects including brain dysfunction and attention problems continue well after that, says Prof Goodfellow.

Alcohol causes the most harm on complex brain functions, explains Prof Susan J Astley from the University of Washington. This is why its impact may not be obvious until later in life, she says. In fact, there are human studies showing that prenatal exposure to even low doses of alcohol may be harmful.

It's hard to prove impacts from light drinking

If light drinking has consequences, why is human evidence still lacking? The truth is, it's difficult to prove small effects. FASD effects can be mild to start with. This may be the reason why it is often undiagnosed, says Dr Montag. It also explains why it has been so tricky to demonstrate that light drinking can be harmful. You would expect effects to be less severe with low doses, and those subtle changes will be easier to miss. Plus, self-reporting is not always reliable as explained by Prof Jennie Connorfrom the University of Otago. Recall bias could kick in, she says, and this is particularly hard with low volumes of alcohol.

Experts say some pregnancies are affected by light drinking while others are not. Why? Different people process alcohol differently, argues Dr Montag. On top of variation between individuals, she says, timing and pattern of the drinking, nutritional status or any previous conditions can all play a role.

Can low doses of alcohol harm the baby?

In pregnant women, according to Dr Montag, alcohol can cross the placenta and reach the fetus’ bloodstream directly. Once there, it can cause malformations and abnormalities. Alcohol can also mess up with a number of molecules that are required for brain development. This includes altering gene expression of the CHRNA5 receptor, which leads to abnormal development of the frontal cortex. It also prevents the action of angiotensin IV, a molecule that promotes memory consolidation, and disrupts the function of the L1 cell adhesion molecule, which is involved in the formation of connections between brain cells, explains Prof Michael Charness from Harvard.

What can be done?

Stigma is not the solution, clear public health guidelines are. Because many pregnancies are unplanned, embryos may be exposed to alcohol well before their mums know they are pregnant. Hence, the advice should be for women to avoid drinking if they are trying to get pregnant. If alcohol exposure has already occurred, a caring and stimulating environment for the newborn baby — alongside early diagnosis and intervention — could ameliorate the effects, argues Dr Montag.

Takeaway:

Prenatal exposure to alcohol can have long-term effects — but this is preventable. Experts say no dose is guaranteed to be 100% safe. Stay away from alcohol if you are pregnant or plan to be. How about a mocktail to celebrate?

Stay safe and may the facts be with you!

Ben McNeil, Founder of Metafact

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