Two mechanisms, two windows. Between gestational day 17 and 22, before most women have tested, alcohol switches on a cell-death signal in the cells building the face; where enough die you get the signature: smooth philtrum, thin upper lip, narrowed eyes 1. The brain is a slower target, killed and mis-wired through both later trimesters 2. No shared dose threshold, no single window, so the answer covers all three trimesters.
The low-dose question is the only one still open, and the honest answer isn't "safe." Miscarriage risk climbs from the very first drink, about 6% per drink per week, with no floor below which it goes flat 3. One or two glasses a week look harmless in the data only because light drinkers are wealthier and better-educated, and their kids score higher for reasons unrelated to the wine. Strip that confounding out with a genetic natural experiment and even modest first-trimester drinking shows a small, real drop in childhood IQ 4. Its apparent safety is absence of evidence, not evidence of absence 5.
The trigger is "could be pregnant," well before "confirmed pregnant." The face-building window opens roughly two weeks after a missed period, before most tests come back positive 6.
If you drank before you knew, tell your obstetrician plainly. Honest disclosure gets the child screened early, the single biggest protective factor there is 7.
The visible cases are the tip. The child with the small head and flattened face gets diagnosed at birth. The larger group reads normal until around age five, when a teacher starts using words like "regulation" and "impulse," and by second grade there's a diagnosis nobody flagged during the pregnancy. Among fetal-alcohol adults followed longest, most have a mental-health diagnosis, most don't live independently, and roughly one in eight has ever held a job 8.
The fine print — when to skip it, and what people get wrong
"A glass of red is fine, especially late on." The third trimester is peak growth for the cerebellum and hippocampus; the brain hides its damage where the face can't 4.
"FAS only happens to alcoholics." The community study finding up to five per cent of first-graders affected wasn't run in skid row 9.
"I'll cut down." Half-measures keep the risk; the miscarriage curve rises continuously, so the target is zero 3.
Shame that ends prenatal care. Avoiding appointments makes every later outcome worse. Tell the obstetrician anyway.
- 1Smith SM, Garic A, Flentke GR, Berres ME (2014). Neural crest development in fetal alcohol syndrome. Birth Defects Research Part C: Embryo Today: Reviews. link
- 2Popova S, Charness ME, Burd L, et al. (2023). Fetal alcohol spectrum disorders. Nature Reviews Disease Primers. link
- 3Sundermann AC, Zhao S, Young CL, et al. (2019). Alcohol Use in Pregnancy and Miscarriage: A Systematic Review and Meta-Analysis. Alcoholism: Clinical and Experimental Research. link
- 4Zuccolo L, Lewis SJ, Davey Smith G, et al. (2013). Prenatal alcohol exposure and offspring cognition and school performance. A 'Mendelian randomization' natural experiment. International Journal of Epidemiology. link
- 5Mamluk L, Edwards HB, Savovic J, et al. (2017). Low alcohol consumption and pregnancy and childhood outcomes: time to change guidelines indicating apparently 'safe' levels of alcohol during pregnancy? A systematic review and meta-analyses. BMJ Open. link
- 6CDC (2024). About Alcohol Use During Pregnancy. link
- 7ACOG (2024). Tobacco and Substance Use in Pregnancy — Alcohol (ACOG patient and clinician guidance). link
- 8Streissguth AP, Barr HM, Kogan J, Bookstein FL (1996). Understanding the Occurrence of Secondary Disabilities in Clients with Fetal Alcohol Syndrome (FAS) and Fetal Alcohol Effects (FAE): Final Report to the CDC. link
- 9May PA, Chambers CD, Kalberg WO, et al. (2018). Prevalence of Fetal Alcohol Spectrum Disorders in 4 US Communities. JAMA. link
Alcohol in Pregnancy
Heavy and binge-pattern exposure is decisively teratogenic; every major guideline body (ACOG, CDC, RCOG, WHO, NHMRC, Health Canada) converges on universal abstention (ACOG 2024; CDC 2024; RCOG 2018). Mechanism well-characterised at the cellular level (Sulik et al. 1981; Smith et al. 2014); FAS prevalence 14.6 per 10,000 globally (Popova et al. 2017); 1.1–5.0% FASD in mainstream US communities (May et al. 2018); Mendelian-randomization confirms a small but real low-dose cognitive decrement (Zuccolo et al. 2013).
Avoidance protects against a graded, dose-dependent ~6%-per-drink-per-week increase in miscarriage risk with no observed lower threshold (Sundermann et al. 2019) and against the elevated rates of preterm birth, small-for-gestational-age, low birthweight, and perinatal mortality seen in alcohol-exposed pregnancies (Strandberg-Larsen et al. 2022, OR for SGA 2.20; Patra et al. 2011). The reader experiences this as the difference between a pregnancy that carries to term with a healthy newborn versus the cascade of pregnancy-loss and early-delivery outcomes — substantial within months.
Nine to ten months of social abstention. Mechanically trivial — you simply don't pour the drink — but socially non-zero in cultures where wine at dinner is the default and the absence is noticed. Non-alcoholic substitutes remove most of the friction; the residual cost is the social-coordination work.
Prenatal alcohol exposure is the leading preventable cause of non-genetic intellectual disability worldwide (Popova et al. 2023). Streissguth's 25-year longitudinal cohort found by adulthood ~90% of FAS individuals carry a psychiatric diagnosis, ~80% do not live independently, ~60% have legal trouble (Streissguth et al. 1996). The mortality and morbidity prevented are largely the child's, but the multi-decade burden lands on the family.
Avoidance reduces the long-tail mental-health burden FASD imposes on the family (≥90% psychiatric comorbidity in FAS adults; Streissguth et al. 1996) and spares the maternal grief associated with preventable miscarriage or stillbirth. Modest and largely indirect, but real.