Prevention

There is only a simple answer to this which is to avoid drinking alcohol all together whilst pregnant. Although some studies have shown moderate drinking might not cause a risk, the royal colleges publish these guidlines:

The Royal College of Obstetricians and Gynaecologists recommend in their green top guide that alcohol should be avoided completely whilst trying for a baby and whilst pregnant. They recommend if you do drink to have no more than 1-2 units once or twice a week and to avoid binge drinking all together.                                                                                                The Royal College of Midwives recommend that no alcohol should be consumed whilst trying for a baby or during a pregnancy. Although they state that no evidence has been found that low levels of alcohol use are harmful after the first trimester.

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