Module 3: Risk Factors for FASD
Timing of Alcohol Consumption
Timing of alcohol consumption can affect fetal development. As expected, heavy drinking (four or more drinks in a day at least occasionally) throughout pregnancy can cause major structural defects to the fetus.2 These include defects in
several major organ systems, growth retardation, and brain abnormalities. However,
different systems are more vulnerable at different times.
During specific stages of brain development, such as those that occur in early pregnancy, the fetus is especially vulnerable.3,4
If a woman binge drinks during a critical stage, the fetal brain
can be harmed significantly. The resulting deficits can include CNS structural
abnormalities, such as small brain size and altered brain circuitry. These alterations
can lead to attention deficits, impulse control
problems, hyperactivity, and other serious behavioral consequences. 5
The following figures show the differences in the brain size in newborn rats exposed to alcohol in different concentrations. Group A received 4.5 g/kg of body weight over 4 hours each
day. Group B received 4.5 g/kg over 8 hours each day. Group C received 6.6 g/kg over
a 24-hour-period each day. Control animals received no alcohol. The results suggest
that higher peaks in BAC are associated with greater reductions in brain weight.6
The specific type of birth defect depends on the systems in the fetus developing at the
time of alcohol exposure.6-8 Organ systems are most vulnerable to damage by alcohol during
the period of most dynamic development. The damage seen in animal models roughly corresponds
to weeks 3 to 8 in human pregnancy.6-8 However, if a woman drinks any time throughout her pregnancy, damage may occur. For example:
- Heavy alcohol exposure during the period of craniofacial development will affect facial features. This roughly corresponds to the third and fourth weeks of human pregnancy.
- The structure of the kidneys is most vulnerable around the sixth week of pregnancy.8
- Skeletal malformations can occur during weeks 3 to 8, such as incomplete growth of forelimbs and defects of the digits.6
- Heart defects can occur from alcohol exposure as early as weeks 3 to 4.6,8
Vulnerability of the Fetus to Defects During Different Periods of Development
Current knowledge suggests that growth is more affected during the last trimester than any other
time. Alcohol consumption at any point can put a fetus at risk for growth deficiencies. However,
a woman who drinks moderately to heavily during the third trimester is even more at risk of having
a child with growth deficiencies. These alterations can lead to attention deficits, impulse control problems, hyperactivity, and other serious behavioral consequences.
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