Pregnant women increase the risk of miscarriage if they drink ANY alcohol at all during the first three months of pregnancy.
That's the latest message from experts who also say that women who are trying to conceive should stay tee-total.
The revised advice comes from the Royal College of Obstetricians and Gynaecologists whose previous guidance stated that mothers-to-be should not drink more than two units once or twice per week.
It said there is no proven safe amount that women can drink during pregnancy and the only way to be certain that the baby is not harmed by alcohol is not to drink at all during pregnancy or while breastfeeding.
However the new guidance says that small amounts of alcohol after the first trimester don't appear to be harmful.
After this time women are advised to not drink more than one to two units, more than once or twice a week.
The guidance states that drinking alcohol around conception and during the first three months of pregnancy risks miscarriage.
Drinking may also affect the unborn baby as some will pass through the placenta and into its bloodstream.
This can affect the baby's development, in particular the way its brain develops and how it grows in the womb.
This can lead to foetal growth restriction, increase the risk of stillbirth and premature labour.
It could also result in foetal alcohol spectrum disorder and the more severe foetal alcohol syndrome, which can lead to children having physical and mental disabilities.
Chairwoman of the RCOG's Patient Information Committee, Philippa Marsden, said: "For women planning a family, it is advisable not to drink during this time. Either partner drinking heavily can make it more difficult to conceive.
"During early pregnancy, the safest approach is to abstain from alcohol and after the first trimester keep within the recommended amounts if you do decide to have an alcohol drink. The same applies for women who decide to breastfeed.
"If you cut down or stop drinking at any point during pregnancy, it can make a difference to your baby. However, in some instances, once the damage has been done, it cannot be reversed."
Ann Furedi, chief executive of the British Pregnancy Advisory Service, urged women not to be unduly concerned if they drank alcohol before realising they were pregnant.
She said: "It may be wise to avoid alcohol when planning a baby, but the fact is many pregnancies are not planned.
"We should reassure women that if they have had an episode of binge-drinking before they found out they were pregnant, they really should not worry.
"It is very troubling to see women so concerned about the damage they have caused their baby they consider ending what would otherwise be a wanted pregnancy, when there's no need for such anxiety.
"This guidance also makes clear that, after the first three months, there is no evidence of harm to the baby at low levels of alcohol, so women who like to relax with a glass of wine once or twice a week should not feel guilty about doing so."
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