The Alcohol Pharmacology Education Partnership: When Can Alcohol Damage the Fetus?

Prenatal alcohol exposure can damage the fetus during the entire pregnancy, but depending on when the exposure occurs determines which organ is affected. Pregnancy can be subdivided into three trimesters, each about twelve weeks long. Important events in fetal development occur during each of these trimesters.

The majority of structural development takes place during the first trimester (the 1st twelve weeks of pregnancy). During the first trimester the musculoskeletal system is formed, along with the internal organ systems (for example, the endocrine system, respiratory tract, digestive tract, and the nervous system). The stage in development when organs are formed is referred to as organogenesis. Prenatal alcohol exposure during the first trimester can cause damage to specific cell populations crucial to organ formation. Some of the most common physical defects include facial abnormalities, small skull circumference, skeletal and muscle problems, and problems with internal organs.

An unfortunate reality is that during the early stages of the first trimester many women do not realize they are pregnant, and if they drink alcohol, they may unknowingly cause structural damage (skeletal and organ) to their unborn child.

Alcohol exposure at during the first trimester is not limited to skeletal and organ damage. Damage to the brain occurs as well, leading to cognitive and behavioral problems.

Alcohol-induced brain damage can occur at any time during pregnancy (and during breast-feeding as well!). During all 3 trimesters (and beyond), the major cells of the brain, the neurons and glia, are formed from stem cells (neurogenesis and gliogenesis, respectively). Then, neurons multiply, grow and establish their branches and connections. The long axons of neurons become surrounded by myelin, which insulates and protects the neurons and allows electrical information to be transmitted along the axon. When a pregnant mother drinks alcohol during periods of neurogenesis, the alcohol actually kills the neural stem cells, reducing neurogenesis. Thus, the fetus can still develop neuronal abnormalities leading to behavioral and learning deficits, without any manifestation of the physical abnormalities described above.

Learn more about neurogenesis and alcohol

Learn more about neurogenesis

module 05 figure 07Figure 5.7 The stages of development of the brain and spinal cord over the 3 trimesters are shown. Alcohol affects brain development during all 3 trimesters.

There is a common misconception that the absence of facial abnormalities means that the child’s exposure to alcohol was minimal and therefore the child has a milder form of FAS. On the contrary, drinking during the second and third trimesters can produce children with severe cognitive and behavioral problems in the absence of facial abnormalities.

Alcohol consumed throughout pregnancy (during all three trimesters), can cause a wide variety of effects on the fetus, ranging from brain damage to musculoskeletal damage and growth retardation. In cases of episodic binge drinking (once in a while), injury to the brain and other organs may be more selective. Damage to specific organs (including the brain) will depend on whether the particular organ is undergoing a significant step in development or a growth spurt at the time when alcohol consumption takes place.

Alcohol exposure at any time during pregnancy can cause damage to the fetal brain.

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