To the Editor: Further to the letter by Batagol1 regarding the National Health and Medical Research Council (NHMRC) guidelines on alcohol consumption during pregnancy,2 I believe that the guidelines should emphasise the basic principles of embryology and teratology. The first 2 weeks after conception (2–4 weeks after the last prepregnancy menstrual period, when women are unaware that they have conceived) are known as the “all-or-none period” — a phase during which teratogens will either cause non-viability or do no harm at all. Exposure to teratogens during this period does not cause birth defects because the cleavage-stage embryo consists of undifferentiated stem cells without significant vascular connection to the maternal circulation. Thus, women can always be reassured after such early alcohol exposure.3
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