Any alcohol which is drunk by the mother passes directly to the baby via the placenta. Alcohol is a teratogen which means it is a substance which can change the structure and function of developing organs.

The baby experiences the same effects as the mother – but because their internal organs are much smaller, the alcohol actually stays in their systems for much longer and causes more damage. It was once thought that the placenta filtered toxins to protect the baby but we now now that this is not the case. 

The baby's brain and central nervous system, which continues to grow throughout gestation, is susceptible to the damaging effects of alcohol at any stage of pregnancy. See chart below – sourced with thanks from Mother to Baby – specialists on teratogens in the USA.