Drinking alcohol during pregnancy can cause a range of permanent physical and cognitive problems in the baby, collectively known as fetal alcohol spectrum disorders (FASDs). No amount of alcohol has been established as safe at any stage of pregnancy. The effects range from subtle learning difficulties to severe birth defects, depending on how much alcohol is consumed, how often, and when during the pregnancy it occurs. Up to 1 in 20 U.S. school-aged children may fall somewhere on the fetal alcohol spectrum.
How Alcohol Reaches the Baby
When you drink, alcohol passes from your bloodstream through the placenta and into the baby’s blood. The baby’s developing body processes alcohol far more slowly than yours, so alcohol concentrations in the baby’s blood stay elevated longer. This prolonged exposure is what causes damage.
Alcohol disrupts the formation and migration of brain cells. It interferes with the signaling that guides neurons to their correct positions and damages the blood vessel networks the developing brain depends on. It also depletes key proteins involved in building brain tissue, reducing white matter volume in ways that show up on brain scans years later. These aren’t temporary setbacks. They’re structural changes that persist into adulthood.
What Can Happen in the First Trimester
The first 12 weeks carry the highest risk for physical malformations because this is when the body’s organ systems are being laid out. The heart, brain, eyes, kidneys, and facial structures all begin forming in rapid succession, and alcohol can derail any of these processes. If damage is severe enough, it can end the pregnancy entirely.
Between weeks three and eight, cranial neural crest cells are shaping the baby’s face. Alcohol exposure during this window produces the characteristic facial features of fetal alcohol syndrome: a smooth groove between the nose and upper lip, a thin upper lip, and short eye openings. These specific features are diagnostic markers, meaning they’re used to identify the most severe form of FASD.
Heart defects are another first-trimester risk. Alcohol disrupts the cells responsible for building the heart’s chambers and valves, potentially causing atrial and ventricular abnormalities and increasing the risk of heart disease later in life. Eye development also begins early, and alcohol exposure during weeks three through five can damage the retina, the optic nerve, or the structures that form the lens and cornea. By weeks six and seven, the corpus callosum, the bridge connecting the brain’s two hemispheres, becomes vulnerable. Alcohol can cause it to be underdeveloped or missing altogether.
Risks in the Second and Third Trimesters
The brain continues growing and organizing throughout the entire pregnancy, which means alcohol can cause neurological damage at any point. Later exposure is more likely to affect brain growth, behavior, and birth weight than to cause the structural organ defects seen in the first trimester. Low birthweight and behavioral problems are associated with alcohol use at any stage.
The good news is that stopping alcohol at any point during pregnancy improves outcomes. Because brain development is ongoing, every week without alcohol exposure gives the baby’s nervous system a better chance to develop normally.
Pregnancy Complications
Beyond direct harm to the baby, alcohol increases the risk of losing the pregnancy. Women who drink during pregnancy are 40% more likely to experience stillbirth compared to women who abstain. That risk climbs with the amount consumed: five or more drinks per week raises the stillbirth risk by 70%. Early stillbirth specifically is 80% more likely among women who drink.
Moderate to heavy drinking in the first trimester is also linked to increased rates of miscarriage. Frequent alcohol use during the first eight weeks can trigger spontaneous abortion alongside the organ-level damage happening in the embryo.
Fetal Alcohol Spectrum Disorders
FASD is an umbrella term covering several diagnoses, ranging from mild to severe.
- Fetal alcohol syndrome (FAS) is the most severe form. It involves all three hallmarks: distinctive facial features, growth problems (lower than average height or weight), and central nervous system damage. Children with FAS often struggle with learning, memory, attention, communication, vision, and hearing.
- Partial fetal alcohol syndrome (pFAS) is diagnosed when a child has confirmed prenatal alcohol exposure and some, but not all, of the FAS features.
- Alcohol-related neurodevelopmental disorder (ARND) involves intellectual disabilities and problems with behavior and learning, but without the physical features of FAS. Children with ARND often struggle with math, memory, attention, judgment, and impulse control. This is harder to diagnose because there are no visible markers.
- Alcohol-related birth defects (ARBD) involves physical problems with the heart, kidneys, bones, or hearing, without the full FAS picture.
Prevalence estimates vary depending on how diagnoses are made. When researchers use medical records alone, about 1 in every 1,000 infants is identified with FAS. But when researchers examine school-aged children in person, the numbers jump to 6 to 9 per 1,000. The full range of FASDs, including milder forms, is estimated at 1% to 5% of school-aged children in the U.S. and some Western European countries.
Long-Term Cognitive Effects
Prenatal alcohol exposure causes deficits in executive function that persist throughout life. Executive function is the set of mental skills you use to plan, focus attention, remember instructions, and manage impulses. Children affected by prenatal alcohol often struggle in school not because they lack intelligence in a general sense, but because they can’t organize their thinking, control their behavior, or hold information in working memory the way their peers can.
Brain imaging studies show that children with FASD have reduced white matter volume, the tissue that connects different brain regions and allows them to communicate efficiently. Over time, both affected and unaffected children gain white matter and improve cognitive performance, but children with FASD depend more heavily on those structural brain gains to make cognitive progress. Their brains have less built-in reserve, so any disruption to development has outsized consequences.
What If You Drank Before Knowing You Were Pregnant
This is one of the most common concerns, and it’s worth addressing directly. Many pregnancies are unplanned, and many women drink alcohol in the weeks before a positive test. The risk from early, unintentional exposure depends heavily on the amount and frequency. Occasional light drinking in the earliest days is less likely to cause measurable harm than repeated heavy drinking during the same period.
That said, the embryonic period (weeks three through eight of gestation) is when the face, heart, brain, and kidneys are forming. Frequent or heavy drinking during these weeks can cause the characteristic facial changes of FAS, increase miscarriage risk, and affect organ development. The practical takeaway: if you’ve had a few drinks before finding out you’re pregnant, the most important thing you can do is stop now. The earlier you stop, the better the outcomes for the baby’s brain and body.