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Is There Any Amount of Alcohol That’s Okay to Consume During Pregnancy?

Many of us have been taught that the consumption of alcohol during pregnancy poses myriad risks to a developing fetus. According to the Centers for Disease Control and Prevention (CDC), drinking while pregnant can result in miscarriage and stillbirth, and can increase a baby’s risk of birth defects, developmental delays, or lifelong behavioral, intellectual, and physical disabilities.1

But just how much alcohol during pregnancy is required to cause these potentially adverse outcomes? And is the advice doled out by virtually all public health institutions and most American doctors that women should completely eschew alcohol for the entirety of their pregnancies based on solid evidence?2 Or is this guidance an overly cautious attempt to curtail adverse outcomes that lack a substantial scientific consensus?

What We Know About Drinking During Pregnancy

It’s clear from decades of research that binge drinking (four or more servings of alcohol at a time, five or more times per month) significantly increases a woman’s risk of bearing a child with any of several fetal alcohol spectrum disorders (or FASDs).3 FASDs refer to a broad range of conditions seen in infants and children who were exposed to alcohol in the womb. They encompass physical abnormalities and disabilities, emotional and behavioral problems, and cognitive and intellectual deficits.

Women who drink at such excessive levels one or more times during the second or third trimester have been found across numerous studies to be more likely to bear offspring with language delays.4 There is evidence that excessive alcohol consumption during pregnancy alters babies’ expression of genes that regulate circadian rhythms and stress reactions.5 Excessive drinking in the first trimester increases the likelihood of offspring physical deformities, like a very thin upper lip (“thin vermillion border”), no ridges of flesh between the nose and upper lip (“smooth philtrum”), an abnormally small head (microcephaly), and reduced birth weight.6

How Alcohol Affects a Fetus 

To get to fetal cells in the first place, alcohol must first move through a pregnant person’s digestive system, where the alcohol is absorbed via epithelial cells in the stomach and small intestine, into the bloodstream.7 The person feels alcohol’s effects as the substance crosses the blood-brain barrier and binds to receptors for gamma-aminobutyric acid (GABA) and glutamate, and reduces firing between neurons in her brain. The fetus is subjected to alcohol’s effects thanks to the ease with which the substance diffuses across the placenta and into the fetal blood supply.8

A person can usually metabolize the alcohol from one drink within one to two hours, thanks primarily to two enzymes that break the substance down: Alcohol dehydrogenase (ADH), which converts alcohol to a toxic and carcinogenic byproduct called acetaldehyde, and aldehyde dehydrogenase (ALDH), which further breaks down acetaldehyde into acetate. Most alcohol metabolism occurs in the liver. But ADH and ALDH enzymes also exist in smaller concentrations inside the pancreas, stomach, and brain.9

A developing fetus, however, is limited in its ability to metabolize alcohol and its byproducts and in its mother’s ability to eliminate these chemicals from the fetal blood supply. So alcohol, acetaldehyde, and aldehyde can linger in the fetal blood supply, granting these compounds more time to achieve potentially deleterious effects on fetal cells.

Alcohol can damage cells in several ways. It can interfere with how genes are transcribed and translated during the cycle of cellular growth and division, thereby inhibiting cell growth—especially the growth of brain cells, or neurons.  It can impair other cellular processes, like the synthesis of ATP, and trigger cell death (or apoptosis). And its metabolism increases the concentration of reactive oxygen species (e.g., ROS) within cells that can further damage the structural components of cells as well as DNA.10

It is this potential damage wrought by alcohol upon cells that are thought to account for why mothers who drink excessively during pregnancy face a higher risk of bearing offspring with physical, intellectual, or behavioral problems. Alcohol’s ability to kill off and damage cells can greatly impair the developing nervous systems of babies, risking mild to severe brain damage and physical deformity.

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